Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Detail)

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Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 0 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2014
Dec. 31, 2013
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Awards Outstanding, Beginning Balance         12,143,000  
Granted, Awards         1,610,000  
Exercised, Awards         (832,000)  
Forfeited, Awards         (99,000)  
Awards Outstanding, Ending Balance 12,822,000 12,143,000 12,822,000   12,822,000  
Awards Exercisable, Ending Balance 8,238,000   8,238,000   8,238,000  
Weighted Average Exercise Price Outstanding, Beginning Balance         $ 33.24  
Granted, Weighted Average Exercise Price         $ 59.56  
Exercised, Weighted Average Exercise Price         $ 21.05  
Forfeited, Weighted Average Exercise Price         $ 58.55  
Weighted Average Exercise Price Outstanding, Ending Balance $ 37.14 $ 33.24 $ 37.14   $ 37.14  
Exercisable, Weighted Average Exercise Price, Ending Balance $ 25.57   $ 25.57   $ 25.57  
Weighted Average Remaining Contractual Term Outstanding 5 years 2 months 12 days 5 years 3 months 18 days        
Weighted Average Remaining Contractual Term Exercisable 3 years 8 months 12 days          
Aggregate Intrinsic Value Outstanding, Beginning balance         $ 552.9  
Aggregate Intrinsic Value Outstanding, Ending balance 172.3 552.9 172.3   172.3  
Exercisable, Aggregate Intrinsic Value, Ending Balance $ 169.3   $ 169.3   $ 169.3  
Granted, Weighted Average Grant Date Fair Value     $ 20.88 $ 0.00 $ 25.71 $ 11.85
Incentive Plan And Independent Directors Stock Units [Member]
            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Outstanding and nonvested December 31, 2013, Shares         144,500  
Granted, Shares         28,100  
Vested, Shares         (134,600)  
Forfeited, Shares         (4,100)  
Outstanding and nonvested at September 30, 2014, Shares 33,900   33,900   33,900  
Outstanding and nonvested December 31, 2013, Weighted Average Grant Date Fair Value         $ 14.36  
Granted, Weighted Average Grant Date Fair Value         $ 59.98  
Vested, Weighted Average Grant Date Fair Value         $ 10.76  
Forfeited, Weighted Average Grant Date Fair Value         $ 38.58  
Outstanding and nonvested at September 30, 2014, Weighted Average Grant Date Fair Value $ 63.61   $ 63.61   $ 63.61