Capital Structure (Details) (USD $) In Millions, except Share data, unless otherwise specified			0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Noncumulative Perpetual Preferred Stock, Series E	Mar. 31, 2014 Noncumulative Perpetual Preferred Stock, Series E
Preferred stock
Preferred stock, issued shares	72,200	32,300	10,000	29,900
Preferred stock, par value (in dollars per share)	$ 1	$ 1	$ 1.00	$ 1.00
Preferred stock, shares liquidation preference (in dollars per share)			$ 25,000	$ 25,000
Gross proceeds from issue of preferred stock			$ 250.0	$ 747.5
Note stated interest rate (as a percent)			6.25%	6.625%