Weighted Average Common Shares - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Repurchase of outstanding common stock	6,500,000,000
Number of shares purchased	62,900,000
Shares purchased value	5,300,000,000
Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares granted	1,118,043	1,016,801
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	2,876,887
Performance Share Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares granted	362,873	292,662
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	1,139,268	292,662
Equity Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares granted	521,773	162,911
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	6,790,531	3,371,122