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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Guaranteed Minimum Benefits [Line Items]
Net premiums earned	$ 7,935	$ 8,327	$ 7,891	$ 7,137	$ 7,465	$ 7,908	$ 7,664	$ 7,027	$ 31,290	$ 30,064	$ 29,034
Policy benefits and other reserve adjustments	$ 225	$ 158	$ 161	$ 196	$ 162	$ 127	$ 150	$ 151	740	590	676
Guaranteed Minimum Death Benefit
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									41	47	49
Policy benefits and other reserve adjustments									0	20	40
GLB
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									92	96	110
Policy benefits and other reserve adjustments									122	110	105
Realized Investment Gains (Losses)									(6)	(250)	363
Gain (loss) recognized in income									(36)	(264)	368
Net cash received									0	47	65
Net (increase) decrease in liability									$ (36)	$ (311)	$ 303