Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Credit Derivatives [Line Items]
Notional Amount	$ 15	$ 4
Average Term (Years)	0 years	0 years
Payment / Performance Risk	0.00%	0.00%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 15	$ 4
Average Term (Years)	3 years 29 days	6 years 5 months 27 days
Payment / Performance Risk	6.64%	17.93%