Loans and Allowance for Credit Losses, PCI Loans Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Dec. 31, 2008
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	$ 21,555	$ 23,320
Total PCI loans (unpaid principal balance)	30,369	32,924	$ 98,200
Total Commercial [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	873	1,507	18,700
Commercial and Industrial Loans [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	86	75
Commercial Real Estate Mortgage [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	681	1,261
Commercial Real Estate Construction [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	106	171
Total Consumer [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	20,682	21,813	$ 40,100
Real estate 1-4 family first mortgage [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	20,601	21,712
Real estate 1-4 family junior lien mortgage [Member]
PCI loans [Abstract]
Purchased Credit Impaired Loans (carrying value)	$ 81	$ 101