Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	$ 20	$ 26
Cumulative effect of adopting ASU 2014-01 [Member] | Low Income Housing Tax Credit Investments [Member]
Operating Loss Carryforwards [Line Items]
Amortization recognized for low income housing tax credits associated with adoption of ASU 2014-01	52
Tax credits recognized for low income housing tax credits associated with adoption of ASU 2014-01	56
Other tax benefits recognized for low income housing tax credits associated with adoption of ASU 2014-01	19
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Loss Carryforwards	2,249	2,272
Tax Credit Carryforward Valuation Allowance	$ 61
Operating Loss Carryforwards Earliest Expiration Date	2016
Operating Loss Carryforwards Latest Expiration Date	2036
Reduction of state net operating losses	$ 60
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Net Operating Loss Carryforwards	$ 858	$ 878
Operating Loss Carryforwards Expiration Date	Dec. 31, 2032
Tax Credit Carryforward Expiration Date	Dec. 31, 2032
Income Tax Examination Earliest Year Complete	2007
Income Tax Examination Latest Year Complete	2010
Income Tax Examination Earliest Year Under Examination	2011
Income Tax Examination Latest Year Under Examination	2013
Internal Revenue Service (IRS) [Member] | National City Acquisition [Member]
Operating Loss Carryforwards [Line Items]
Income Tax Returns National City Year Settled	2008