Income Taxes - Components of U.S. and Foreign Income and Reconciliation between Federal Income Tax Expense at Statutory Rates and Actual Income Tax Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income before income tax:
Income before income tax, U.S.	$ 543	$ 1,499	$ 1,945
Income before income tax, Foreign	(299)	311	332
Income before income tax	244	1,810	2,277
Income tax expense at statutory rate	86	633	797
Increase (decrease) in income tax expense resulting from:
Exempt investment income	(126)	(121)	(99)
Foreign related tax differential	(18)	(48)	(117)
Amortization of deferred charges associated with intercompany rig sales to other tax jurisdictions	38	44	31
Taxes related to domestic affiliate	(10)	14	19
Partnership earnings not subject to taxes	(38)	(39)	(38)
Unrecognized tax benefit (expense)	1	(42)	66
Other	24	16	(3)
Income tax expense (benefit)	$ (43)	$ 457	$ 656