AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	$ (837)	$ (748)	$ (1,028)	$ (751)
OCI before reclassifications, net of tax	79	(90)	269	(145)
Amounts reclassified from AOCI:
Personnel expense	1,006	882	2,960	2,576
Interest income	(1,795)	(1,650)	(5,321)	(4,632)
Interest expense	185	186	565	544
FDIC loss share income, net	18	58	142	201
(Gain) loss on securities, net	0	2	(45)	3
Income before income taxes	(915)	(755)	(2,570)	(2,124)
Less: Income taxes	(273)	(222)	(771)	(543)
Net income	(642)	(533)	(1,799)	(1,581)
Net change in AOCI	87	(48)	278	(45)
AOCI, ending balance	(750)	(796)	(750)	(796)
Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Personnel expense	18	14	51	38
Interest income	(1)	24	(43)	31
Interest expense	(3)	21	18	63
FDIC loss share income, net	0	7	33	26
(Gain) loss on securities, net	0	2	(45)	3
Income before income taxes	14	68	14	161
Less: Income taxes	6	26	5	61
Net income	8	42	9	100
Unrecognized Net Pension and Postretirement Costs
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(701)	(608)	(723)	(626)
OCI before reclassifications, net of tax	(9)	(23)	(8)	(20)
Amounts reclassified from AOCI:
Net change in AOCI	2	(14)	24	4
AOCI, ending balance	(699)	(622)	(699)	(622)
Unrecognized Net Pension and Postretirement Costs | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Personnel expense	18	14	51	38
Interest income	0	0	0	0
Interest expense	0	0	0	0
FDIC loss share income, net	0	0	0	0
(Gain) loss on securities, net	0	0	0	0
Income before income taxes	18	14	51	38
Less: Income taxes	7	5	19	14
Net income	11	9	32	24
Unrealized Net Gains (Losses) on Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(247)	(35)	(83)	(54)
OCI before reclassifications, net of tax	23	(105)	(154)	(112)
Amounts reclassified from AOCI:
Net change in AOCI	21	(92)	(143)	(73)
AOCI, ending balance	(226)	(127)	(226)	(127)
Unrealized Net Gains (Losses) on Cash Flow Hedges | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Personnel expense	0	0	0	0
Interest income	0	0	0	0
Interest expense	(3)	21	18	63
FDIC loss share income, net	0	0	0	0
(Gain) loss on securities, net	0	0	0	0
Income before income taxes	(3)	21	18	63
Less: Income taxes	(1)	8	7	24
Net income	(2)	13	11	39
Unrealized Net Gains (Losses) on AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	263	102	(34)	152
OCI before reclassifications, net of tax	(72)	36	280	(18)
Amounts reclassified from AOCI:
Net change in AOCI	(73)	51	224	1
AOCI, ending balance	190	153	190	153
Unrealized Net Gains (Losses) on AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Personnel expense	0	0	0	0
Interest income	(2)	22	(45)	28
Interest expense	0	0	0	0
FDIC loss share income, net	0	0	0	0
(Gain) loss on securities, net	0	2	(45)	3
Income before income taxes	(2)	24	(90)	31
Less: Income taxes	(1)	9	(34)	12
Net income	(1)	15	(56)	19
FDIC's Share of Unrealized (Gains) Losses on AFS Securities
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(137)	(188)	(169)	(207)
OCI before reclassifications, net of tax	137	5	148	12
Amounts reclassified from AOCI:
Net change in AOCI	137	9	169	28
AOCI, ending balance	0	(179)	0	(179)
FDIC's Share of Unrealized (Gains) Losses on AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Personnel expense	0	0	0	0
Interest income	0	0	0	0
Interest expense	0	0	0	0
FDIC loss share income, net	0	7	33	26
(Gain) loss on securities, net	0	0	0	0
Income before income taxes	0	7	33	26
Less: Income taxes	0	3	12	10
Net income	0	4	21	16
Other, net
AOCI, Net of Tax [Roll Forward]
AOCI, beginning balance	(15)	(19)	(19)	(16)
OCI before reclassifications, net of tax	0	(3)	3	(7)
Amounts reclassified from AOCI:
Net change in AOCI	0	(2)	4	(5)
AOCI, ending balance	(15)	(21)	(15)	(21)
Other, net | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Personnel expense	0	0	0	0
Interest income	1	2	2	3
Interest expense	0	0	0	0
FDIC loss share income, net	0	0	0	0
(Gain) loss on securities, net	0	0	0	0
Income before income taxes	1	2	2	3
Less: Income taxes	1	1	1	1
Net income	$ 0	$ 1	$ 1	$ 2