Derivative Financial Instruments - Derivative Netting (Details) $ in Millions	Mar. 31, 2019 USD ($) party	Dec. 31, 2018 USD ($) party
Credit Derivatives
Number of counter-parties (in Party) | party	5	4
Notional amount	$ 296	$ 306
Credit exposure	8	9
Exposure, net of collateral	$ 2	$ 1
A plus
Credit Derivatives
Number of counter-parties (in Party) | party	4	3
Notional amount	$ 268	$ 283
Credit exposure	8	9
Exposure, net of collateral	$ 1	$ 1
A
Credit Derivatives
Number of counter-parties (in Party) | party	1	1
Notional amount	$ 28	$ 23
Credit exposure	0	0
Exposure, net of collateral	$ 1	$ 0