Schedule Summarizing Quarterly Operation Results (Detail) (USD $) In Millions, except Per Share data, 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
Quarterly Financial Information [Line Items]
Total revenues	$ 9,557	$ 9,651	$ 9,699	[1]	$ 10,219	$ 9,056	$ 9,301	$ 9,284	$ 9,191	$ 39,126	$ 36,832	$ 33,596
Income before income taxes	282	675	564	[1]	390	313	699	726	497	1,911	2,235	1,749
Net income	$ 192	$ 426	$ 356	[1]	$ 248	$ 199	$ 445	$ 460	$ 315	$ 1,222	$ 1,419	$ 1,099
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

[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.