Reinsurance Reinsurance (Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts - Schedule Of Guaranteed Minimum Benefits Income And Expense) (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Guaranteed Minimum Benefits [Line Items]
Net premiums earned	$ 7,465	$ 7,908	$ 7,664	$ 7,027	$ 7,218	$ 7,807	$ 7,237	$ 6,772	$ 30,064	$ 29,034	$ 28,749
Policy benefits and other reserve adjustments	$ 162	$ 127	$ 150	$ 151	$ 176	$ 169	$ 163	$ 168	590	676	588
Guaranteed Minimum Death Benefit
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									47	49	55
Policy benefits and other reserve adjustments									20	40	45
Guaranteed Minimum Income Benefit
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									96	110	118
Policy benefits and other reserve adjustments									110	105	52
Realized Investment Gains (Losses)									(250)	363	48
Gain (loss) recognized in income									(264)	368	114
Net cash received									47	65	79
Net (increase) decrease in liability									$ (311)	$ 303	$ 35