Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	$ (318)	$ (124)	$ (69)
Other comprehensive income before reclassification	(41)	(214)
Amounts reclassified from accumulated other comprehensive income	(10)	(31)
Net current-period other comprehensive income	(51)	(245)
Ending balance	(369)	(369)	(69)
Unrealized Gains (Losses) on Available for Sale Securities [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	82	229
Other comprehensive income before reclassification	(81)	(228)
Amounts reclassified from accumulated other comprehensive income
Net current-period other comprehensive income	(81)	(228)
Ending balance	1	1
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	(21)	18
Other comprehensive income before reclassification	20	(2)
Amounts reclassified from accumulated other comprehensive income	(10)	(27)
Net current-period other comprehensive income	10	(29)
Ending balance	(11)	(11)
Foreign Currency Translation Adjustment [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	41	55
Other comprehensive income before reclassification	2	(8)
Amounts reclassified from accumulated other comprehensive income		(4)
Net current-period other comprehensive income	2	(12)
Ending balance	43	43
Net Pension and Postretirement Benefit Costs [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	(420)	(426)
Other comprehensive income before reclassification	18	24
Amounts reclassified from accumulated other comprehensive income
Net current-period other comprehensive income	18	24
Ending balance	$ (402)	$ (402)