Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Notional Amount	$ 358	$ 134
Average Term (Years)	0 years	0 years
Payment / Performance Risk	0.00%	0.00%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 358	$ 134
Average Term (Years)	14 years 7 months 13 days	14 years 3 months 18 days
Payment / Performance Risk	27.09%	14.56%