Derivative Financial Instruments and Off-balance sheet Financial Instruments - OTC derivatives counterparty credit exposure (Details) $ in Millions	Dec. 31, 2020 USD ($) counter-party	Dec. 31, 2019 USD ($) counter-party
Credit Derivatives
Number of counter-parties | counter-party	3	6
Notional amount	$ 280	$ 868
Credit exposure	7	29
Exposure, net of collateral	0	0
Gross liability fair value of contracts containing credit-risk-contingent features	27	16
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(9)	(11)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(17)	(3)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 1	$ 2
A plus
Credit Derivatives
Number of counter-parties | counter-party	3	6
Notional amount	$ 280	$ 868
Credit exposure	7	29
Exposure, net of collateral	$ 0	$ 0