Federal and Foreign Income Tax - Income Tax Expense and Taxes Paid (Detail) (USD $) In Millions, 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
Income tax expense and taxes paid
Current tax, United States									$ 276	$ 260	$ 436
Current tax, Foreign									143	236	242
Deferred tax, principally United States									32	25	136
Federal and foreign income tax	(39)	194	123	173	150	68	127	176	451	521	814
Federal and foreign income taxes paid									$ 472	$ 598	$ 500