Schedule of Details Supporting Computation of Earnings Per Share (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available for common stockholders	$ 192	$ 426	$ 356	[1]	$ 248	$ 199	$ 445	$ 460	$ 315	$ 1,222	$ 1,419	$ 1,099
Weighted-average outstanding shares of common stock used to compute basic earnings per common share										161,484	165,413	167,782
Shares used to compute diluted earnings per common share										163,457	167,827	169,798
Basic earnings per common share	$ 1.21	$ 2.65	$ 2.19	[1]	$ 1.51	$ 1.22	$ 2.71	$ 2.76	$ 1.88	$ 7.56	$ 8.58	$ 6.55
Diluted earnings per common share	$ 1.19	$ 2.62	$ 2.16	[1]	$ 1.49	$ 1.20	$ 2.67	$ 2.71	$ 1.86	$ 7.47	$ 8.46	$ 6.47
Number of antidilutive stock options and restricted stock awards excluded from computation										754	864	3,820
Employee Stock Options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock										576	959	676
Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock										1,397	1,455	1,340

[1] Includes an expense of $46 million ($29 million after tax, or $0.18 per diluted common share) for a litigation settlement associated with our military services business.