Derivatives (Estimated Fair Value of Derivative Assets and Liabilities after Master Netting Agreements and Cash Collateral) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 9,130	$ 8,595
Derivative Liability, Fair Value, Gross Liability	5,745	6,521
Amounts offset in the consolidated balance sheet, Assets	0	0
Amounts offset in the consolidated balance sheet, Liabilities	0	0
Netting [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	9,363	8,850
Derivative Liability, Fair Value, Gross Liability	5,793	6,549
Estimated fair value of derivative assets presented in the consolidated balance sheets	9,363	8,850
Estimated fair value of derivative liabilities presented in the consolidated balance sheets	5,793	6,549
Net amount of derivative assets after application of master netting agreements and cash collateral	221	139
Net amount of derivative liabilities after application of master netting agreements and cash collateral	200	269
Netting [Member] | Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	9,103	8,537
Derivative Liability, Fair Value, Gross Liability	5,391	6,367
Gross estimated fair value of derivative assets	(4,255)	(4,631)
Gross estimated fair value of derivative liabilities	(4,255)	(4,631)
Cash collateral on derivative assets	(2,437)	(1,679)
Cash collateral on derivative liabilities	(3)	(3)
Securities collateral on derivative assets	(2,193)	(2,105)
Securities collateral on derivative liabilities	(933)	(1,464)
Netting [Member] | Exchange Traded [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	6	11
Derivative Liability, Fair Value, Gross Liability	78	53
Gross estimated fair value of derivative assets	(5)	(5)
Gross estimated fair value of derivative liabilities	(5)	(5)
Cash collateral on derivative assets	0	0
Cash collateral on derivative liabilities	(60)	(44)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	(13)	(4)
Netting [Member] | Cleared [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	254	302
Derivative Liability, Fair Value, Gross Liability	324	129
Gross estimated fair value of derivative assets	(156)	(122)
Gross estimated fair value of derivative liabilities	(156)	(122)
Cash collateral on derivative assets	(96)	(169)
Cash collateral on derivative liabilities	(168)	(7)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	$ 0	$ 0