Income Taxes - Components of U.S. and Foreign Income and Reconciliation between Federal Income Tax Expense at Statutory Rates and Actual Income Tax Expense (Benefit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income before income tax:
Income before income tax, U.S.	$ 775	$ 1,322	$ 1,207
Income before income tax, Foreign	59	260	(271)
Income before income tax	834	1,582	936
Income tax expense at statutory rate	175	554	328
Increase (decrease) in income tax expense resulting from:
Effect of the Tax Act	(6)	(190)
Exempt investment income	(64)	(134)	(126)
Foreign related tax differential	1	(36)	40
Taxes related to domestic affiliate	(7)	1	(14)
Partnership earnings not subject to taxes	(14)	(51)	(52)
Valuation allowance	12	7	62
Unrecognized tax positions, settlements and adjustments relating to prior years	2	(8)	(42)
State taxes	20	23	18
Other	9	4	6
Income tax expense (benefit)	$ 128	$ 170	$ 220