Derivative Financial Instruments and Off-balance sheet Financial Instruments - OTC derivatives counterparty credit exposure (Details) $ in Millions	Dec. 31, 2019 USD ($) counter-party	Dec. 31, 2018 USD ($) counter-party
Credit Derivatives
Number of counter-parties | counter-party	6	5
Notional amount	$ 868	$ 764
Credit exposure	29	20
Exposure, net of collateral	0	1
Gross liability fair value of contracts containing credit-risk-contingent features	16	11
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(11)	(5)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(3)	(2)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 2	$ 4
A plus
Credit Derivatives
Number of counter-parties | counter-party	6	3
Notional amount	$ 868	$ 643
Credit exposure	29	19
Exposure, net of collateral	$ 0	$ 1
A
Credit Derivatives
Number of counter-parties | counter-party	0	2
Notional amount	$ 0	$ 121
Credit exposure	0	1
Exposure, net of collateral	$ 0	$ 0