Derivative Financial Instruments and Off-balance sheet Financial Instruments - Counterparty credit exposure and other (Details) $ in Millions	Dec. 31, 2019 USD ($) counter-party	Dec. 31, 2018 USD ($) counter-party
Credit Derivatives
Cash and securities pledged as collateral by counterparties	$ 8
Securities pledged as collateral to counterparties	1
Securities pledged in the form of margin deposits	6
Collateral posted under MNAs for contracts containing credit-risk-contingent features	$ 1	$ 0
Number of counter-parties | counter-party	5	4
Notional amount	$ 296	$ 306
Credit exposure	7	9
Exposure, net of collateral	0	1
Gross liability fair value of contracts containing credit-risk-contingent features	4	2
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(3)	(2)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(1)	0
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 0	$ 0
A plus
Credit Derivatives
Number of counter-parties | counter-party	5	3
Notional amount	$ 296	$ 283
Credit exposure	7	9
Exposure, net of collateral	$ 0	$ 1
A
Credit Derivatives
Number of counter-parties | counter-party	0	1
Notional amount	$ 0	$ 23
Credit exposure	0	0
Exposure, net of collateral	$ 0	$ 0