Short-Term Borrowings (Primary Components Of Short-term Borrowings) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Weighted-average interest rate at year-end	0.48%	0.55%
Securities Sold Under Repurchase Agreements
Short-term Debt [Line Items]
Balance	$ 7,953	$ 8,006	$ 8,572
Maximum outstanding at any month-end	11,538	9,306	9,853
Average outstanding during the year	8,436	7,697	9,040
Weighted-average interest rate at year-end	0.00254%	0.06%	0.04%
Weighted-average interest rate during the year	0.01%	0.01%	0.11%
Federal Funds Purchased
Short-term Debt [Line Items]
Balance	19	399	656
Maximum outstanding at any month-end	570	1,145	8,259
Average outstanding during the year	297	784	845
Weighted-average interest rate at year-end	0.13%	0.13%	0.05%
Weighted-average interest rate during the year	0.02%	0.09%	0.05%
Tax-Exempt Investment Program
Short-term Debt [Line Items]
Balance	1,948	2,148	2,294
Maximum outstanding at any month-end	2,135	2,274	2,473
Average outstanding during the year	2,030	2,214	2,404
Weighted-average interest rate at year-end	0.09%	0.17%	0.18%
Weighted-average interest rate during the year	0.13%	0.21%	0.26%
Corporate Commercial Paper Program
Short-term Debt [Line Items]
Balance	1,819	2,318	2,384
Maximum outstanding at any month-end	2,535	2,503	2,825
Average outstanding during the year	$ 1,632	$ 2,382	$ 2,449
Weighted-average interest rate at year-end	0.14%	0.22%	0.22%
Weighted-average interest rate during the year	0.18%	0.23%	0.23%