Derivatives (Estimated Fair Value of Derivative Assets and Liabilities after Master Netting Agreements and Cash Collateral) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 9,301	$ 13,777
Derivative Liability, Fair Value, Gross Liability	5,558	5,536
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	9,501	14,067
Derivative Liability, Fair Value, Gross Liability	5,607	5,650
Estimated fair value of derivative assets presented in the consolidated balance sheets	9,501	14,067
Estimated fair value of derivative liabilities presented in the consolidated balance sheets	5,607	5,650
Net amount of derivative assets after application of master netting agreements and cash collateral	337	0
Net amount of derivative liabilities after application of master netting agreements and cash collateral	284	42
Netting [Member] | Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	9,252	14,048
Derivative Liability, Fair Value, Gross Liability	5,443	5,480
Gross estimated fair value of derivative assets	(4,308)	(4,562)
Gross estimated fair value of derivative liabilities	(4,308)	(4,562)
Cash collateral on derivative assets	(2,336)	(5,960)
Cash collateral on derivative liabilities	(3)	(1)
Securities collateral on derivative assets	(2,299)	(3,526)
Securities collateral on derivative liabilities	(848)	(875)
Netting [Member] | Exchange Traded [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	35	19
Derivative Liability, Fair Value, Gross Liability	11	170
Gross estimated fair value of derivative assets	(7)	(19)
Gross estimated fair value of derivative liabilities	(7)	(19)
Cash collateral on derivative assets	0	0
Cash collateral on derivative liabilities	(4)	(151)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	0	0
Netting [Member] | Cleared [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	214	0
Derivative Liability, Fair Value, Gross Liability	153	0
Gross estimated fair value of derivative assets	(147)	0
Gross estimated fair value of derivative liabilities	(147)	0
Cash collateral on derivative assets	(67)	0
Cash collateral on derivative liabilities	(6)	0
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	$ 0	$ 0