Investments - Rollforward of credit loss allowance for fixed income securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fixed income securities
Credit Losses on Fixed Income Securities
Beginning balance	$ 0
Credit losses on securities for which credit losses not previously reported	4	$ 2
Ending balance	(4)
Corporate
Credit Losses on Fixed Income Securities
Credit losses on securities for which credit losses not previously reported	1	0
Ending balance	(1)
ABS
Credit Losses on Fixed Income Securities
Credit losses on securities for which credit losses not previously reported	0	1
MBS
Credit Losses on Fixed Income Securities
Credit losses on securities for which credit losses not previously reported	3	$ 1
Ending balance	$ (3)