Variable Interest Entities (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Variable Interest Entities [Abstract]
Investment securities related to state and political subdivisions	$ 2,330,000,000	$ 2,680,000,000
Variable interest entity, other short-term borrowings	1,950,000,000	2,150,000,000
Weighted average life of trusts (in years)	6 years 6 months	6 years 11 months
Total standby bond-purchase agreement committed to trusts	1,990,000,000
Letters of credit amounts outstanding	684,000,000
Standby purchase agreements and letters of credit commitments utilized	0
Variable Interest Entity [Line Items]
Potential maximum loss exposure of unconsolidated funds	18,000,000	28,000,000
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Potential maximum loss exposure of unconsolidated funds	$ 50,000,000