Derivatives and Hedging Activities - Fair Value of Derivative Assets by Type (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Derivative assets before collateral	$ 564	$ 646
Less: Related collateral	33	(23)
Total derivative assets	531	669
Interest Rate [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	308	401
Foreign Exchange Contract [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	60	77
Commodity [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	187	163
Credit [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	0	1
Other Credit Derivatives [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	$ 9	$ 4