Summary of Significant Accounting Policies (Mortgage Servicing and Transfers of Financial Assets) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Servicing Asset at Amortized Cost [Line Items]
Aggregate unpaid principal balance	$ 4,310,000,000	$ 4,060,000,000
Term of commercial servicing rights	20 years	20 years
Commercial Servicing Rights more than 20 Years
Servicing Asset at Amortized Cost [Line Items]
Servicing rights, valuation allowance	$ 33,000	$ 0