Income Taxes - Provision for Federal & Foreign Income Tax Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current
Operations	$ 975	$ (189)	$ 1,327
One-time charge due to tax legislation	(6)	43	0
Deferred
Operations	(194)	1,607	(261)
One-time charge due to tax legislation	(37)	1,843	0
Total federal income tax expense	738	3,304	1,066
Foreign income tax expense (benefit):
Current	67	53	56
Deferred	(13)	(1)	(29)
Total foreign income tax expense	54	52	27
Total income tax expense	$ 792	$ 3,356	$ 1,093