Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		$ 550	$ 183	$ 550		$ 183	$ 414	$ 135	$ 384	$ 298
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax		310	107	310		107	237	87	141	97
Accumulated Other Comprehensive Income (Loss), Financial Instruments, net of tax		(7)	0	(7)		0	(7)	0	0	0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax		(620)	(584)	(620)		(584)	(623)	(682)	(590)	(517)
Accumulated Other Comprehensive Income (Loss), Net of Tax		233	(294)	233		(294)	$ 21	$ (460)	$ (65)	$ (122)
Cumulative effect of credit risk adjustment				0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		139	(192)	418		(106)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		113	5	305		83
Credit Risk Adjustment		0	0	(2)	[1]	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax		0	0	0		0
Other Comprehensive Income (Loss), Total Unrealized Gain (Loss) Arising During Period, Net of Tax		252	(187)	721		(23)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax		(3)	(9)	(3)		(9)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		(40)	(39)	(82)		(73)
Other Comprehensive Income Loss Reclassfication Adjustment From AOCI on Long Term Debt, Net of Tax		0	0	0		0
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax		3	6	62		(67)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(40)	(42)	(23)		(149)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax		136	(201)	415		(115)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax		73	(34)	223		10
Other Comprehensive Income Loss Long Term Debt, Net of Tax				(2)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax		3	6	62		(67)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent		$ 212	$ (229)	698		$ (172)
AOCI Attributable to Parent [Member]
Cumulative effect of credit risk adjustment	[2],[3]			$ (5)

[1] 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 17, "Accumulated Other Comprehensive Income/(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, beginning January 1, 2016. See Note 1, "Significant Accounting Policies," and Note 17, "Accumulated Other Comprehensive Income/(Loss)," 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.