Derivatives (Estimated Fair Value of Derivative Assets and Liabilities after Master Netting Agreements and Cash Collateral) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Offsetting Assets [Line Items]
Gross estimated fair value of derivative assets	$ 12,743	$ 13,707
Gross estimated fair value of derivative liabilities	6,994	7,082
Amounts offset in the consolidated balance sheet, Assets	0	0
Amounts offset in the consolidated balance sheet, Liabilities	0	0
Estimated fair value of derivative assets presented in the consolidated balance sheets	12,743	13,707
Estimated fair value of derivative liabilities presented in the consolidated balance sheets	6,994	7,082
Net amount of derivative assets after application of master netting agreements and cash collateral	645	324
Net amount of derivative liabilities after application of master netting agreements and cash collateral	160	102
Over the Counter [Member]
Offsetting Assets [Line Items]
Gross estimated fair value of derivative assets	11,486	12,256
Gross estimated fair value of derivative liabilities	5,961	6,017
Gross estimated fair value of derivative assets	(4,434)	(4,082)
Gross estimated fair value of derivative liabilities	(4,434)	(4,082)
Cash collateral on derivative assets	(4,492)	(4,153)
Cash collateral on derivative liabilities	(11)	(133)
Securities collateral on derivative assets	(1,973)	(3,768)
Securities collateral on derivative liabilities	(1,356)	(1,700)
Cleared [Member]
Offsetting Assets [Line Items]
Gross estimated fair value of derivative assets	1,200	1,380
Gross estimated fair value of derivative liabilities	1,006	1,054
Gross estimated fair value of derivative assets	(882)	(989)
Gross estimated fair value of derivative liabilities	(882)	(989)
Cash collateral on derivative assets	(306)	(386)
Cash collateral on derivative liabilities	(118)	(62)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	(6)	(3)
Exchange-traded
Offsetting Assets [Line Items]
Gross estimated fair value of derivative assets	57	71
Gross estimated fair value of derivative liabilities	27	11
Gross estimated fair value of derivative assets	(11)	(5)
Gross estimated fair value of derivative liabilities	(11)	(5)
Cash collateral on derivative assets	0	0
Cash collateral on derivative liabilities	(13)	(4)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	$ (3)	$ (2)