Accumulated Other Comprehensive Income - Changes in AOCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 10,759
Total other comprehensive income (loss), net of tax	(136)	$ (49)	$ (4)
Ending Balance	15,240	10,759
Unrealized Gains (Losses) on Securities Available for Sale [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(58)	(4)
Other comprehensive income before reclassification, net of income taxes	(127)	(127)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	0	0
Total other comprehensive income (loss), net of tax	(127)	(54)
Ending Balance	(185)	(58)	(4)
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	20	(8)
Other comprehensive income before reclassification, net of income taxes	17	87
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	(51)	(59)
Total other comprehensive income (loss), net of tax	(34)	28
Ending Balance	(14)	20	(8)
Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(2)	22
Other comprehensive income before reclassification, net of income taxes	(1)	(25)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	0	1
Total other comprehensive income (loss), net of tax	(1)	(24)
Ending Balance	(3)	(2)	22
Net Pension and Postretirement Benefit Costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(365)	(366)
Other comprehensive income before reclassification, net of income taxes	5	(24)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	21	25
Total other comprehensive income (loss), net of tax	26	1
Ending Balance	(339)	(365)	(366)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(405)	(356)	(352)
Other comprehensive income before reclassification, net of income taxes	(106)	(16)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	(30)	(33)
Total other comprehensive income (loss), net of tax	(136)	(49)
Ending Balance	$ (541)	$ (405)	$ (356)