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, 2013	Dec. 31, 2012
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 12,823	$ 13,777
Derivative Liability, Fair Value	5,294	5,536
Netting [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	13,094	14,067
Derivative Liability, Fair Value	5,437	5,650
Estimated fair value of derivative assets presented in the consolidated balance sheets	13,094	14,067
Estimated fair value of derivative liabilities presented in the consolidated balance sheets	5,437	5,650
Net amount of derivative assets after application of master netting agreements and cash collateral	259	0
Net amount of derivative liabilities after application of master netting agreements and cash collateral	95	42
Netting [Member] | Over the Counter [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	13,091	14,048
Derivative Liability, Fair Value	5,414	5,480
Gross estimated fair value of derivative assets	(4,548)	(4,562)
Gross estimated fair value of derivative liabilities	(4,548)	(4,562)
Cash collateral on derivative assets	(3,912)	(5,960)
Cash collateral on derivative liabilities	(2)	(1)
Securities collateral on derivative assets	(4,372)	(3,526)
Securities collateral on derivative liabilities	(769)	(875)
Netting [Member] | Exchange Traded [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	3	19
Derivative Liability, Fair Value	23	170
Gross estimated fair value of derivative assets	(3)	(19)
Gross estimated fair value of derivative liabilities	(3)	(19)
Cash collateral on derivative assets	0	0
Cash collateral on derivative liabilities	(20)	(151)
Securities collateral on derivative assets	0	0
Securities collateral on derivative liabilities	$ 0	$ 0