Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2012
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	$ (162)	$ (124)	$ (72)
Other comprehensive income before reclassification	(149)	(173)
Amounts reclassified from accumulated other comprehensive income	(7)	(21)
Net current-period other comprehensive income	(156)	(194)
Ending balance	(318)	(318)	(72)
Unrealized Gains (Losses) on Available for Sale Securities [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	207	229
Other comprehensive income before reclassification	(125)	(147)
Net current-period other comprehensive income	(125)	(147)
Ending balance	82	82
Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	10	18
Other comprehensive income before reclassification	(24)	(22)
Amounts reclassified from accumulated other comprehensive income	(7)	(17)
Net current-period other comprehensive income	(31)	(39)
Ending balance	(21)	(21)
Foreign Currency Translation Adjustment [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	44	55
Other comprehensive income before reclassification	(3)	(10)
Amounts reclassified from accumulated other comprehensive income		(4)
Net current-period other comprehensive income	(3)	(14)
Ending balance	41	41
Net Pension and Postretirement Benefit Costs [Member]
Accumulated Comprehensive Income Loss [Line Items]
Beginning balance	(423)	(426)
Other comprehensive income before reclassification	3	6
Net current-period other comprehensive income	3	6
Ending balance	$ (420)	$ (420)