Investments (AFS contractual maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due within one year	$ 620
Due after one year through five years	4,170
Due after five years through 10 years	2,471
Due after 10 years	3,964
Total having single maturity dates	11,225
Amortized cost	18,974
Fair Value
Due within one year	622
Due after one year through five years	4,163
Due after five years through 10 years	2,553
Due after 10 years	4,625
Total having single maturity dates	11,963
Total fair value	19,742
Residential mortgage backed securities [Member]
Amortized Cost
Without single maturity dates	3,107
Amortized cost	3,107	$ 3,039
Fair Value
Without single maturity dates	3,178
Total fair value	3,178	3,108
Commercial mortgage backed securities [Member]
Amortized Cost
Without single maturity dates	3,613
Amortized cost	3,613	3,526
Fair Value
Without single maturity dates	3,638
Total fair value	3,638	3,618
Asset backed securities [Member]
Amortized Cost
Without single maturity dates	1,029
Amortized cost	1,029	1,036
Fair Value
Without single maturity dates	963
Total fair value	$ 963	$ 1,080