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	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income (loss) before income tax:
Income (loss) before income tax, U.S.	$ (142)	$ 129	$ (103)	$ 266
Income (loss) before income tax, Foreign	(134)	166	22	134
Income (loss) before income tax	(276)	295	(81)	400
Income tax expense (benefit) at statutory rate	(97)	103	(28)	140
Increase (decrease) in income tax expense resulting from:
Exempt investment income	(33)	(29)	(64)	(58)
Foreign related tax differential	63	(32)	23	(5)
Valuation allowance	77		77
Amortization of deferred charges associated with intercompany rig sales to other tax jurisdictions		4		41
Taxes related to domestic affiliate	(2)	4	1	(6)
Partnership earnings not subject to taxes	(11)	(7)	(28)	(20)
Unrecognized tax benefit	5	2	10	5
Other	10	3	17	7
Income tax expense	$ 12	$ 48	$ 8	$ 104