Accumulated Other Comprehensive Income - Changes in AOCI (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (352)	$ (124)
Other comprehensive income before reclassification, net of income taxes	16	(216)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	(20)	(12)
Net current-period other comprehensive income, net of income taxes	(4)	(228)	(96)
Ending balance	(356)	(352)	(124)
Unrealized Gains (Losses) on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(63)	229
Other comprehensive income before reclassification, net of income taxes	59	(291)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)		(1)
Net current-period other comprehensive income, net of income taxes	59	(292)
Ending balance	(4)	(63)
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(11)	18
Other comprehensive income before reclassification, net of income taxes	43	6
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	(40)	(35)
Net current-period other comprehensive income, net of income taxes	3	(29)
Ending balance	(8)	(11)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	42	55
Other comprehensive income before reclassification, net of income taxes	(17)	(9)
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	(3)	(4)
Net current-period other comprehensive income, net of income taxes	(20)	(13)
Ending balance	22	42
Net Pension and Postretirement Benefit Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(320)	(426)
Other comprehensive income before reclassification, net of income taxes	(69)	78
Amounts reclassified from accumulated other comprehensive income, net of income taxes (a)	23	28
Net current-period other comprehensive income, net of income taxes	(46)	106
Ending balance	$ (366)	$ (320)