Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Notional Amount	$ 287	$ 134
Payment / Performance Risk	0.00%	0.00%
Other
Credit Derivatives [Line Items]
Notional Amount	$ 287	$ 134
Average Term (Years)	13 years 5 months 23 days	14 years 3 months 18 days
Payment / Performance Risk	17.15%	14.56%