Investments (Continuous Gross Unrealized Losses for Fixed Maturity Securities AFS by Sector) (Details) $ in Millions	Jun. 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	$ 1,323	$ 10,450
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	40	465
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	1,224	2,290
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	46	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	99	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	58	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	105	1,550
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	1	21
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	1,378	2,567
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	13	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	740	3,916
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	27	199
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	743	746
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	70	107
CMBS
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	78	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	262	800
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	4	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	5	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	36	158
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	1	8
ABS
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value of securities in an unrealized loss position for less than 12 months	560	1,407
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	4	21
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	357	70
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	5	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	54	520
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	3	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	2,964	20,812
Gross Unrealized Losses of securities in an unrealized loss position for less than 12 months	$ 75	$ 797
Total number of securities in an unrealized loss position for less than 12 months	639	2,988
Estimated Fair Value of securities in an unrealized loss position for 12 months or greater	$ 4,058	$ 8,118
Gross Unrealized Losses of securities in an unrealized loss position for 12 months or greater	$ 139	$ 552
Total number of securities in an unrealized loss position for 12 months or greater	511	1,022