Investments (AFS contractual maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 879
Due after one year through five years	4,348
Due after five years through 10 years	2,521
Due after 10 years	4,083
Total having single maturity dates	11,831
Amortized cost	20,338
Fair Value
Due within one year	888
Due after one year through five years	4,633
Due after five years through 10 years	2,801
Due after 10 years	5,409
Total having single maturity dates	13,731
Total fair value	22,619
Residential mortgage backed securities [Member]
Amortized Cost
Without single maturity dates	3,195
Amortized cost	3,195	$ 3,039
Fair Value
Without single maturity dates	3,315
Total fair value	3,315	3,108
Commercial mortgage backed securities [Member]
Amortized Cost
Without single maturity dates	4,026
Amortized cost	4,026	3,526
Fair Value
Without single maturity dates	4,247
Total fair value	4,247	3,618
Asset backed securities [Member]
Amortized Cost
Without single maturity dates	1,286
Amortized cost	1,286	1,036
Fair Value
Without single maturity dates	1,326
Total fair value	$ 1,326	$ 1,080