Investments (Continuous Gross Unrealized Losses for Fixed Maturity Securities AFS by Sector) (Details) $ in Millions	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
U.S. corporate
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	$ 1,541	$ 10,450
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	42	465
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	404	2,290
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	32	194
U.S. government and agency
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	75	359
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	0	7
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	0	1,355
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	0	103
RMBS
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	524	1,550
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	3	21
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	411	2,567
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	4	99
Foreign corporate
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	831	3,916
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	28	199
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	581	746
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	81	107
CMBS
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	102	2,264
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	0	52
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	190	800
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	3	34
State and political subdivision
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	15	346
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	0	7
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	8	158
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	0	8
ABS
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	445	1,407
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	3	21
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	504	70
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	7	1
Foreign government
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	52	520
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	5	25
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	0	132
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	0	6
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	3,585	20,812
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	$ 81	$ 797
Total number of securities in an unrealized loss position for less than 12 months	669	2,988
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	$ 2,098	$ 8,118
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	$ 127	$ 552
Total number of securities in an unrealized loss position for 12 months or greater	309	1,022