Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		$ (60)	$ 414	$ (62)	$ 135
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax		(199)	237	(157)	87
Accumulated Other Comprehensive Income (Loss), Financial Instruments, net of tax		(1)	0	(1)	0
Accumulated Other Comprehensive Income (Loss), Long-term Debt, Net of Tax		(8)	(7)	(7)	0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax		(599)	(623)	(594)	(682)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(867)	21	$ (821)	$ (460)
Cumulative effect of credit risk adjustment	[1]		0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		2	279
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		(16)	192
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Brokered Time Deposits Arising During Period, Net of Tax		0	0
Other Comprehensive Income (Loss), Unrealized Credit Risk Gain (Loss) on Long-term Debt Arising During Period, Net of Tax		(1)	(2)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax		0	0
Other Comprehensive Income (Loss), Total Unrealized Gain (Loss) Arising During Period, Net of Tax		(15)	469
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		(26)	(42)
Other Comprehensive Income (Loss), Reclassification from AOCI on Brokered Time Deposits, Net of Tax		0	0
Other Comprehensive Income Loss Reclassfication Adjustment From AOCI on Long Term Debt, Net of Tax		0	0
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax		(5)	59
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(31)	17
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		2	279
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		(42)	150
Other Comprehensive Income (Loss), Brokered Time Deposits, Net of Tax		0	0
Other Comprehensive Income (Loss), Long Term Debt, Adjustment, Net of Tax	[2]	1	2
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax		(5)	59
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ (46)	486
AOCI Attributable to Parent [Member]
Cumulative effect of credit risk adjustment	[1],[3]		$ (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 18, "Accumulated Other Comprehensive (Loss)/Income," 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," and Note 18, "Accumulated Other Comprehensive (Loss)/Income," for additional information.

[3] 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.