Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		$ (1)	$ (62)	$ 135	$ 298
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax		(244)	(157)	87	97
Accumulated Other Comprehensive Income (Loss), Brokered Time Deposits, net of tax		(1)	(1)	0	0
Accumulated Other Comprehensive Income (Loss), Long-term Debt, Net of Tax		(4)	(7)	0	0
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax		(570)	(594)	(682)	(517)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(820)	(821)	(460)	$ (122)
Cumulative Effect of Credit Risk Adjustment	[1]		0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		(7)	(194)	(150)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		(31)	(91)	154
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Brokered Time Deposits Arising During Period, Net of Tax		0	(1)	0
Other Comprehensive Income (Loss), Unrealized Credit Risk Gain (Loss) on Long-term Debt Arising During Period, Net of Tax		3	(2)	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax		11	76	(174)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(24)	(212)	(170)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		68	(3)	(13)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		(56)	(153)	(164)
Other Comprehensive Income (Loss), Reclassification from AOCI on Brokered Time Deposits, Net of Tax		0	0	0
Other Comprehensive Income Loss Reclassfication Adjustment From AOCI on Long Term Debt, Net of Tax		0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax		13	12	9
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		25	(144)	(168)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		61	(197)	(163)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(87)	(244)	(10)
Other Comprehensive Income (Loss), Brokered Time Deposits, Net of Tax		0	(1)	0
Other Comprehensive Income (Loss), Long Term Debt, Adjustment, Net of Tax		(3)	2	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		(24)	(88)	165
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ 1	(356)	$ (338)
AOCI Attributable to Parent [Member]
Cumulative Effect of Credit Risk Adjustment	[1],[2]		$ (5)

[1] Related to the Company's early adoption of the ASU 2016-01 provision related to changes in instrument-specific credit risk, beginning January 1, 2016. See Note 1, "Significant Accounting Policies," and Note 21, "Accumulated Other Comprehensive Loss," for additional information.

[2] Related to the Company's early adoption of the ASU 2016-01 provision related to changes in instrument-specific credit risk. See Note 1, "Significant Accounting Policies," for additional information.