Securities (Details 3) $ in Millions	Mar. 31, 2017 USD ($)
Securities available for sale
One Year or Less	$ 5
Over One Year Through Five Years	899
Over Five Years Through Ten Years	4,465
Over Ten Years	9,551
Total Fair Value	14,920
U.S. Treasury securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	393
Over Five Years Through Ten Years	2,420
Over Ten Years	0
Total Fair Value	2,813
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	9
Over Five Years Through Ten Years	301
Over Ten Years	7,068
Total Fair Value	7,378
Residential mortgage-backed securities, Privately issued
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	425
Total Fair Value	426
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	0
Over Ten Years	663
Total Fair Value	663
Collateralized loan obligations
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	1,020
Over Ten Years	977
Total Fair Value	1,997
Other Asset Liability Management Securities
Securities available for sale
One Year or Less	1
Over One Year Through Five Years	1
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	1
Over One Year Through Five Years	404
Over Five Years Through Ten Years	3,746
Over Ten Years	9,133
Total Fair Value	13,284
Other debt securities, Direct bank purchase bonds
Securities available for sale
One Year or Less	4
Over One Year Through Five Years	428
Over Five Years Through Ten Years	719
Over Ten Years	392
Total Fair Value	1,543
Other debt securities, Other
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	67
Over Five Years Through Ten Years	0
Over Ten Years	26
Total Fair Value	$ 93