Derivative Financial Instruments - CDS notional amount by credit rating and fair value of protection sold (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Credit derivative, term	5 years
Notional amount	$ 3,858	$ 3,478
Credit default contracts
Derivative [Line Items]
Notional amount	759	9
Fair value	6	0
Single name | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	9	9
Fair value	0	0
Corporate debt | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	750
Fair value	6
AAA | Credit default contracts
Derivative [Line Items]
Notional amount	6	0
AAA | Single name | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	0	0
AAA | Corporate debt | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	6
AA | Credit default contracts
Derivative [Line Items]
Notional amount	12	0
AA | Single name | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	0	0
AA | Corporate debt | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	12
A | Credit default contracts
Derivative [Line Items]
Notional amount	156	0
A | Single name | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	0	0
A | Corporate debt | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	156
BBB | Credit default contracts
Derivative [Line Items]
Notional amount	492	0
BBB | Single name | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	0	0
BBB | Corporate debt | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	492
BB and lower | Credit default contracts
Derivative [Line Items]
Notional amount	93	9
BB and lower | Single name | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	9	$ 9
BB and lower | Corporate debt | Corporate | Credit default contracts
Derivative [Line Items]
Notional amount	$ 84