Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		$ (519)	$ (5)	$ (519)	$ (5)	$ (396)	$ (1)	$ (60)	$ (62)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax		(459)	(168)	(459)	(168)	(424)	(244)	(199)	(157)
Accumulated Other Comprehensive Income (Loss), Brokered Time Deposits, net of tax		(1)	(1)	(1)	(1)	0	(1)	(1)	(1)
Accumulated Other Comprehensive Income (Loss), Long-term Debt, Net of Tax		(2)	(7)	(2)	(7)	(3)	(4)	(8)	(7)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax		(698)	(596)	(698)	(596)	(699)	(570)	(599)	(594)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(1,679)	(777)	(1,679)	(777)	$ (1,522)	$ (820)	$ (867)	$ (821)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[1]			(10)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		(123)	56	(547)	58
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		(47)	48	(172)	32
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Brokered Time Deposits Arising During Period, Net of Tax		(1)	0	0	0
Other Comprehensive Income (Loss), Unrealized Credit Risk Gain (Loss) on Long-term Debt Arising During Period, Net of Tax		1	1	3	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax		(2)	0	(7)	(9)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(172)	105	(723)	81
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		0	(1)	(1)	(1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		12	(17)	13	(43)
Other Comprehensive Income (Loss), Reclassification from AOCI on Brokered Time Deposits, Net of Tax		0	0	0	0
Other Comprehensive Income Loss Reclassfication Adjustment From AOCI on Long Term Debt, Net of Tax		0	0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax		3	3	6	7
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		15	(15)	18	(37)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		(123)	55	(548)	57
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(35)	31	(159)	(11)
Other Comprehensive Income (Loss), Brokered Time Deposits, Net of Tax		(1)	0	0	0
Other Comprehensive Income (Loss), Long Term Debt, Adjustment, Net of Tax		(1)	(1)	(3)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		(1)	(3)	1	2
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ (157)	$ 90	(705)	$ 44
AOCI Attributable to Parent [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[1],[2]			(154)
Available-for-sale Securities [Member] | AOCI Attributable to Parent [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[2]			30
Derivative [Member] | AOCI Attributable to Parent [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[2]			(56)
Brokered Time Deposits [Member] | AOCI Attributable to Parent [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[2]			0
Long-term Debt [Member] | AOCI Attributable to Parent [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[2]			(1)
Defined Benefit Plan [Member] | AOCI Attributable to Parent [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	[2]			$ (127)

[1] Related to the Company's adoption of ASU 2014-09, ASU 2016-01, ASU 2017-12, and ASU 2018-02 on January 1, 2018. See Note 1, "Significant Accounting Policies," for additional information.

[2] Related to the Company's adoption of ASU 2018-02 on January 1, 2018. See Note 1, "Significant Accounting Policies," for additional information.