Derivative Financial Instruments (Notional Amount of Interest Rate Swap Agreements Designated as Fair Value and Cash Flow Hedges) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Derivative [Line Items]
Notional Amount of Fair Value Hedges	$ 4,092		$ 3,023
Notional Amount of Cash Flow Hedges	130		130
Notional amount of derivatives	4,222		3,153
Increase in carrying value of long-term debt	18		174
Investment securities available for sale
Derivative [Line Items]
Notional Amount of Fair Value Hedges	2,592		1,573
Notional Amount of Cash Flow Hedges	130		130
Notional amount of derivatives	2,722		1,703
Long-term debt
Derivative [Line Items]
Notional Amount of Fair Value Hedges	1,500	[1]	1,450	[1]
Notional Amount of Cash Flow Hedges	0	[1]	0	[1]
Notional amount of derivatives	$ 1,500	[1]	$ 1,450	[1]

[1] As of September 30, 2013 and December 31, 2012, fair value hedges of long-term debt increased the carrying value of long-term debt presented in our consolidated statement of condition by $18 million and $174 million, respectively.