Short and Long-Term Funding (Long-term Funding Narrative) (Details) - USD ($)	1 Months Ended
	Nov. 30, 2014	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2011	Mar. 31, 2011
Subordinated Borrowing [Line Items]
Carrying Value of Federal Funds Purchased, Securities Sold under Agreements to Repurchase, and Deposits Received for Securities Loaned		$ 543,000,000
Federal Home Loan Bank, Advances, Weighted Average Interest Rate		0.33%	0.13%
Two Thousand Eleven Senior Notes [Member]
Subordinated Borrowing [Line Items]
New Senior Debt Issued				$ 130,000,000	$ 300,000,000
Debt Instrument, Interest Rate, Stated Percentage					5.125%
Two Thousand Fourteen Senior Notes [Member]
Subordinated Borrowing [Line Items]
New Senior Debt Issued	$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage	2.75%
Two Thousand Fourteen Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Junior Subordinated Debentures Issued	$ 250,000,000
Debt Instrument, Term	10 years
Subordinated Borrowing, Interest Rate	4.25%