Investment Securities (Debt Securities Issued By Corporation) (Details) (Debt securities issued by corporations, USD $)	Dec. 31, 2013		Dec. 31, 2012
Investment securities
Fair value investments	$ 2,347,200,000	[1]	$ 2,385,100,000	[1]
Other Standard Poors Rating [Member]
Investment securities
Fair value investments	3,400,000		6,800,000
Standard & Poor's, BB Rating [Member]
Investment securities
Fair value investments	0		7,000,000
BBB
Investment securities
Fair value investments	1,075,500,000		1,116,900,000
A
Investment securities
Fair value investments	1,039,500,000		1,061,000,000
AA
Investment securities
Fair value investments	228,800,000		193,400,000
AAA
Investment securities
Fair value investments	$ 0		$ 0

[1] Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s