Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Credit Derivatives [Line Items]
Notional Amount	$ 146	$ 227
Payment / Performance Risk	0.00%	0.00%
Other
Credit Derivatives [Line Items]
Notional Amount	$ 146	$ 227
Average Term (Years)	13 years 14 days	12 years 9 months 3 days
Payment / Performance Risk	17.88%	19.53%