Short-Term Borrowings (Primary Components Of Short-term Borrowings) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-term Debt [Line Items]
Weighted-average interest rate at year end	0.64%	1.10%
Conduit Commercial Paper Program [Member]
Short-term Debt [Line Items]
Balance		$ 1,919	$ 12,071	[1]
Maximum outstanding at any month end	271	7,275	15,645	[1]
Average outstanding during the year	113	6,339	10,691	[1]
Weighted-average interest rate at year end		0.57%	1.31%	[1]
Weighted-average interest rate during the year	0.47%	0.32%	1.26%	[1]
Securities Sold Under Repurchase Agreements [Member]
Short-term Debt [Line Items]
Balance	8,572	7,599	10,542
Maximum outstanding at any month end	9,853	9,058	12,993
Average outstanding during the year	9,040	8,108	11,065
Weighted-average interest rate at year end	0.04%	0.04%	0.03%
Weighted-average interest rate during the year	0.11%	0.05%	0.03%
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance	656	7,748	4,532
Maximum outstanding at any month end	8,259	7,748	7,166
Average outstanding during the year	845	1,759	956
Weighted-average interest rate at year end	0.05%	0.01%	0.01%
Weighted-average interest rate during the year	0.05%	0.05%	0.04%
Tax-Exempt Investment Program [Member]
Short-term Debt [Line Items]
Balance	2,294	2,484	2,736
Maximum outstanding at any month end	2,473	2,690	2,838
Average outstanding during the year	2,404	2,594	2,774
Weighted-average interest rate at year end	0.18%	0.37%	0.33%
Weighted-average interest rate during the year	0.26%	0.33%	0.47%
Corporate Commercial Paper Program [Member]
Short-term Debt [Line Items]
Balance	2,384	2,799	2,777
Maximum outstanding at any month end	2,825	2,831	2,851
Average outstanding during the year	$ 2,449	$ 2,791	$ 1,993
Weighted-average interest rate at year end	0.22%	0.31%	0.21%
Weighted-average interest rate during the year	0.23%	0.31%	0.30%

[1] Amounts other than balance and weighted-average interest rate at year-end related to the period subsequent to the May 2009 conduit consolidation.