Fair Value Disclosures (Notional or Contractual Amounts and Fair Values of Off-Balance Sheet Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Residential mortgage loans sold with recourse	$ 702	$ 667
Other loans sold with recourse	4,198	4,264
Letters of credit	3,033	3,462
Notional Or Contract Amount [Member]
Commitments to extend, originate or purchase credit	59,019	49,333
Residential mortgage loans sold with recourse	702	667
Other loans sold with recourse	4,198	4,264
Letters of credit	3,033	3,462
Fair Value [Member]
Commitments to extend, originate or purchase credit	253	238
Residential mortgage loans sold with recourse	8	9
Other loans sold with recourse	7	7
Letters of credit	$ 27	$ 22