Securities (Details 3) $ in Millions	Mar. 31, 2016 USD ($)
Securities available for sale
One Year or Less	$ 67
Over One Year Through Five Years	385
Over Five Years Through Ten Years	3,122
Over Ten Years	9,429
Total Fair Value	13,003
U.S. Treasury
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	152
Over Ten Years	0
Total Fair Value	152
Residential mortgage-backed securities, U.S. government agency and government-sponsored agencies
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	17
Over Five Years Through Ten Years	372
Over Ten Years	5,919
Total Fair Value	6,308
Residential mortgage-backed securities, Privately issued
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	3
Over Five Years Through Ten Years	0
Over Ten Years	200
Total Fair Value	203
Privately issued - commercial mortgage-backed securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	37
Over Ten Years	1,455
Total Fair Value	1,492
Collateralized loan obligations
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	16
Over Five Years Through Ten Years	1,858
Over Ten Years	1,353
Total Fair Value	3,227
Other Asset Liability Management Securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	2
Over Five Years Through Ten Years	5
Over Ten Years	0
Total Fair Value	7
Asset Liability Management securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	38
Over Five Years Through Ten Years	2,424
Over Ten Years	8,927
Total Fair Value	11,389
Other debt securities, Direct bank purchase bonds
Securities available for sale
One Year or Less	67
Over One Year Through Five Years	346
Over Five Years Through Ten Years	698
Over Ten Years	470
Total Fair Value	1,581
Other debt securities, Other
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	1
Over Five Years Through Ten Years	0
Over Ten Years	32
Total Fair Value	$ 33