Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic earnings per share:
Net Income	$ 558	$ 594	$ 499	$ 449	$ 569	$ 541	$ 579	$ 656	$ 2,100	$ 2,345	$ 1,545
Weighted average shares outstanding									242.9	258.2	269.5
Basic earnings per share	$ 2.35	$ 2.47	$ 2.03	$ 1.81	$ 2.25	$ 2.11	$ 2.22	$ 2.49	$ 8.65	$ 9.08	$ 5.73
Diluted earnings per share:
Net Income	$ 558	$ 594	$ 499	$ 449	$ 569	$ 541	$ 579	$ 656	$ 2,100	$ 2,345	$ 1,545
Weighted average shares outstanding									242.9	258.2	269.5
Additional shares from assumed issuance of shares under stock-based compensation awards									0.6	1.2	1.9
Weighted average shares and potential shares assumed outstanding for computing diluted earnings per share									243.5	259.4	271.4
Diluted earnings per share	$ 2.35	$ 2.47	$ 2.03	$ 1.80	$ 2.24	$ 2.10	$ 2.21	$ 2.48	$ 8.62	$ 9.04	$ 5.69