Loans and Allowance for Credit Losses, PCI, by Credit Quality Indicator (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Dec. 31, 2008
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	$ 21,555	$ 23,320
Total Commercial [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	873	1,507	$ 18,700
Commercial and Industrial Loans [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	86	75
Commercial Real Estate Mortgage [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	681	1,261
Commercial Real Estate Construction [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	106	171
Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	873	1,507
Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	86	75
Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Mortgage [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	681	1,261
Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	106	171
Pass [Member] | Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	497	922
Pass [Member] | Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	25	21
Pass [Member] | Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Mortgage [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	397	783
Pass [Member] | Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	75	118
Criticized [Member] | Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	376	585
Criticized [Member] | Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	61	54
Criticized [Member] | Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Mortgage [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	284	478
Criticized [Member] | Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
Purchased Credit Impaired Loans by Credit Quality Indicator [Abstract]
Purchased Credit Impaired Loans	$ 31	$ 53