AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amounts reclassified from AOCI:
Total OCI, net of tax		$ (88)	$ (104)	$ (277)
Unrecognized Net Pension and Postretirement Costs
AOCI, net of Tax [Roll Forward]
Beginning balance		(764)	(723)	(626)
OCI before reclassifications, net of tax		(129)	(91)	(139)
Amounts reclassified from AOCI:
Total OCI, net of tax		(84)	(41)	(97)
Ending balance		(1,004)	(764)	(723)
Unrecognized Net Pension and Postretirement Costs | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	72	80	67
Tax effect		27	30	25
Amounts reclassified, net of tax		45	50	42
Reclassification of certain tax effects		(156)
Unrealized Net Gains (Losses) on Cash Flow Hedges
AOCI, net of Tax [Roll Forward]
Beginning balance		(92)	(83)	(54)
OCI before reclassifications, net of tax		7	(16)	(81)
Amounts reclassified from AOCI:
Total OCI, net of tax		18	(9)	(29)
Ending balance		(92)	(92)	(83)
Unrealized Net Gains (Losses) on Cash Flow Hedges | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	15	11	83
Tax effect		4	4	31
Amounts reclassified, net of tax		11	7	52
Reclassification of certain tax effects		(18)
Unrealized Net Gains (Losses) on AFS Securities
AOCI, net of Tax [Roll Forward]
Beginning balance		(259)	(34)	152
OCI before reclassifications, net of tax		(23)	(201)	(206)
Amounts reclassified from AOCI:
Total OCI, net of tax		(27)	(225)	(186)
Ending balance		(356)	(259)	(34)
Unrealized Net Gains (Losses) on AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	(7)	(39)	32
Tax effect		(3)	(15)	12
Amounts reclassified, net of tax		(4)	(24)	20
Reclassification of certain tax effects		(70)
FDIC's Share of Unrealized (Gains) Losses on AFS Securities
AOCI, net of Tax [Roll Forward]
Beginning balance		0	(169)	(207)
OCI before reclassifications, net of tax		0	148	19
Amounts reclassified from AOCI:
Total OCI, net of tax		0	169	38
Ending balance		0	0	(169)
FDIC's Share of Unrealized (Gains) Losses on AFS Securities | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	0	33	31
Tax effect		0	12	12
Amounts reclassified, net of tax		0	21	19
Reclassification of certain tax effects		0
Other, net
AOCI, net of Tax [Roll Forward]
Beginning balance		(17)	(19)	(16)
OCI before reclassifications, net of tax		5	1	(9)
Amounts reclassified from AOCI:
Total OCI, net of tax		5	2	(3)
Ending balance		(15)	(17)	(19)
Other, net | Amounts reclassified from AOCI
Amounts reclassified from AOCI:
Before tax	[1]	0	1	9
Tax effect		0	0	3
Amounts reclassified, net of tax		0	1	6
Reclassification of certain tax effects		(3)
Total
AOCI, net of Tax [Roll Forward]
Beginning balance		(1,132)	(1,028)	(751)
OCI before reclassifications, net of tax		(140)	(159)	(416)
Amounts reclassified from AOCI:
Before tax	[1]	80	86	222
Tax effect		28	31	83
Amounts reclassified, net of tax		52	55	139
Total OCI, net of tax		(88)	(104)	(277)
Reclassification of certain tax effects		(247)
Ending balance		$ (1,467)	$ (1,132)	$ (1,028)

[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 or 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.