AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Amounts reclassified from AOCI:
Net change in AOCI		$ 37	$ 87	$ 96	$ 278
Unrecognized Net Pension and Postretirement Costs
AOCI, Net of Tax [Roll Forward]
Beginning balance		(743)	(701)	(764)	(723)
OCI before reclassifications, net of tax		1	(9)	0	(8)
Amounts reclassified from AOCI:
Net change in AOCI		8	2	29	24
Ending balance		(735)	(699)	(735)	(699)
Unrecognized Net Pension and Postretirement Costs | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	11	18	46	51
Tax effect		4	7	17	19
Amounts reclassified, net of tax		7	11	29	32
Unrealized Net Gains (Losses) on Cash Flow Hedges
AOCI, Net of Tax [Roll Forward]
Beginning balance		(128)	(247)	(92)	(83)
OCI before reclassifications, net of tax		1	23	(26)	(154)
Amounts reclassified from AOCI:
Net change in AOCI		9	21	(27)	(143)
Ending balance		(119)	(226)	(119)	(226)
Unrealized Net Gains (Losses) on Cash Flow Hedges | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	13	(3)	(1)	18
Tax effect		5	(1)	0	7
Amounts reclassified, net of tax		8	(2)	(1)	11
Unrealized Net Gains (Losses) on AFS Securities
AOCI, Net of Tax [Roll Forward]
Beginning balance		(187)	263	(259)	(34)
OCI before reclassifications, net of tax		19	(72)	99	280
Amounts reclassified from AOCI:
Net change in AOCI		18	(73)	90	224
Ending balance		(169)	190	(169)	190
Unrealized Net Gains (Losses) on AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	(2)	(2)	(15)	(90)
Tax effect		(1)	(1)	(6)	(34)
Amounts reclassified, net of tax		(1)	(1)	(9)	(56)
FDIC's Share of Unrealized (Gains) Losses on AFS Securities
AOCI, Net of Tax [Roll Forward]
Beginning balance			(137)		(169)
OCI before reclassifications, net of tax			137		148
Amounts reclassified from AOCI:
Net change in AOCI			137		169
Ending balance			0		0
FDIC's Share of Unrealized (Gains) Losses on AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]		0		33
Tax effect			0		12
Amounts reclassified, net of tax			0		21
Other, net
AOCI, Net of Tax [Roll Forward]
Beginning balance		(15)	(15)	(17)	(19)
OCI before reclassifications, net of tax		2	0	4	3
Amounts reclassified from AOCI:
Net change in AOCI		2	0	4	4
Ending balance		(13)	(15)	(13)	(15)
Other, net | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	0	1	0	2
Tax effect		0	1	0	1
Amounts reclassified, net of tax		0	0	0	1
Total
AOCI, Net of Tax [Roll Forward]
Beginning balance		(1,073)	(837)	(1,132)	(1,028)
OCI before reclassifications, net of tax		23	79	77	269
Amounts reclassified from AOCI:
Net change in AOCI		37	87	96	278
Ending balance		(1,036)	(750)	(1,036)	(750)
Total | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	22	14	30	14
Tax effect		8	6	11	5
Amounts reclassified, net of tax		$ 14	$ 8	$ 19	$ 9

[1] Amounts related to unrecognized net pension and postretirement costs are included in personnel expense, amounts related to unrealized net gains (losses) on cash flow hedges are included in net interest income, amounts related to unrealized net gains (losses) on AFS securities are included in net interest income and securities gains/losses when realized, amounts related to FDIC's share of unrealized gains (losses) on AFS securities are included in FDIC loss share income, net and amounts related to other, net are primarily included in net interest income in the Consolidated Statements of Income.