Derivatives and Hedging Activities - Fair Value of Derivative Assets by Type (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Credit Derivatives [Line Items]
Derivative assets before collateral	$ 646	$ 958
Less: Related collateral	(23)	155
Total derivative assets	669	803
Interest Rate [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	401	782
Foreign Exchange [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	77	62
Commodity [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	163	110
Credit [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	1	0
Other Credit Derivatives [Member]
Credit Derivatives [Line Items]
Derivative assets before collateral	$ 4	$ 4