Fair Values of Assets and Liabilities (Level 3 rollforwards-Assets) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Corporate debt securities [Member]
Summary of changes in Level 3 assets measured at fair value on a recurring basis [Rollforward]
Balance, at the beginning of the period	$ 735	$ 871
Total gains (losses) included in other comprehensive income (loss)	(6)	14
Purchases	6
Settlements	(14)	(71)
Balance, at the end of the period	721	814
Changes in unrealized gains (losses) in OCI relating to assets held at the end of the period	(6)
Residential mortgage backed securities [Member]
Summary of changes in Level 3 assets measured at fair value on a recurring basis [Rollforward]
Balance, at the beginning of the period	17	64
Settlements		(1)
Transfers out of Level 3		(45)
Balance, at the end of the period	17	18
Asset backed securities [Member]
Summary of changes in Level 3 assets measured at fair value on a recurring basis [Rollforward]
Balance, at the beginning of the period	389	374
Total gains (losses) included in other comprehensive income (loss)	(89)	5
Balance, at the end of the period	300	379
Changes in unrealized gains (losses) in OCI relating to assets held at the end of the period	(89)
Total [Member]
Summary of changes in Level 3 assets measured at fair value on a recurring basis [Rollforward]
Balance, at the beginning of the period	1,141	1,309
Total gains (losses) included in other comprehensive income (loss)	(95)	19
Purchases	6
Settlements	(14)	(72)
Transfers out of Level 3		(45)
Balance, at the end of the period	1,038	1,211
Changes in unrealized gains (losses) in net income relating to assets held at the end of the period	0	$ 0
Changes in unrealized gains (losses) in OCI relating to assets held at the end of the period	$ (95)