Investments (EITF info-Fair value) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value [Line Items]
Less than 12 months	$ 5,622	$ 1,079
12 months or more	58	593
Total	5,680	1,672
Corporate debt securities [Member]
Fair Value [Line Items]
Less than 12 months	2,425	64
12 months or more	13	90
Total	2,438	154
Residential mortgage backed securities [Member]
Fair Value [Line Items]
Less than 12 months	1,174	571
12 months or more	8	298
Total	1,182	869
Commercial mortgage backed securities [Member]
Fair Value [Line Items]
Less than 12 months	1,305	310
12 months or more	0	82
Total	1,305	392
State and municipal obligations [Member]
Fair Value [Line Items]
Less than 12 months	79	23
12 months or more	4	54
Total	83	77
Asset backed securities [Member]
Fair Value [Line Items]
Less than 12 months	550	111
12 months or more	23	54
Total	573	165
Foreign government bonds and obligations [Member]
Fair Value [Line Items]
Less than 12 months	89	0
12 months or more	10	15
Total	$ 99	$ 15