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, 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
Income tax expense and taxes paid
Current tax, United States									$ 617	$ 791	$ 276
Current tax, Foreign									124	91	143
Deferred tax, principally United States									20	10	32
Federal and foreign income tax	204	224	179	154	217	198	217	260	761	892	451
Federal and foreign income taxes paid									$ 571	$ 789	$ 472