Investments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 investments	Dec. 31, 2013	Oct. 01, 2014
Investments [Abstract]
Investment in Bancorporation stock			$ 21,600,000
Investment securities, aggregate fair value, continuous unrealized losses of more than 12 months	832,400,000
Investment securities, aggregate unrealized loss, continuous unrealized losses of more than 12 months	10,000,000
Number of investments in continuous unrealized loss position for more than twelve months	86
Unrealized losses related to marketability of securities or issuers ability to honor redemption obligations	0	0
Investment value deemed to be OTTI	0
Investment securities, aggregate carrying value, pledged as collateral	$ 4,370,000,000	$ 2,750,000,000