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	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Derivative [Line Items]
Total	$ 5,222		$ 5,221
Increase in carrying value of long-term debt	3		35
Investment securities available for sale
Derivative [Line Items]
Investment securities available for sale	2,722		2,721
Long-term debt
Derivative [Line Items]
Long-term debt	2,500	[1]	2,500	[1]
Fair Value Hedges
Derivative [Line Items]
Total	5,089		5,089
Fair Value Hedges | Investment securities available for sale
Derivative [Line Items]
Investment securities available for sale	2,589		2,589
Fair Value Hedges | Long-term debt
Derivative [Line Items]
Long-term debt	2,500	[1]	2,500	[1]
Cash Flow Hedges
Derivative [Line Items]
Total	133		132
Cash Flow Hedges | Investment securities available for sale
Derivative [Line Items]
Investment securities available for sale	133		132
Cash Flow Hedges | Long-term debt
Derivative [Line Items]
Long-term debt	$ 0	[1]	$ 0	[1]

[1] As of March 31, 2014, these fair value hedges increased the carrying value of long-term debt presented in our consolidated statement of condition by $3 million. As of December 31, 2013, these fair value hedges decreased the carrying value of long-term debt presented in our consolidated statement of condition by $35 million.