Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		$ 280	$ 339
Other comprehensive income (loss) before reclassifications, after tax		20	274
Reclassification of (gains) losses from accumulated other comprehensive income, after tax			(24)
Other comprehensive income (loss)		20	250
Issuance of equity securities by subsidiary	1	1
Amounts attributable to noncontrolling interests		(3)	(26)
Ending, balance	298	298	563
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		32	23
Transfer to net assets held for sale			(5)
Other comprehensive income (loss) before reclassifications, after tax		(1)	12
Other comprehensive income (loss)		(1)	12
Amounts attributable to noncontrolling interests			(1)
Ending, balance	31	31	29
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		846	622
Transfer to net assets held for sale			(15)
Other comprehensive income (loss) before reclassifications, after tax		119	264
Reclassification of (gains) losses from accumulated other comprehensive income, after tax		(9)	(27)
Other comprehensive income (loss)		110	237
Amounts attributable to noncontrolling interests		(12)	(24)
Ending, balance	944	944	820
Discontinued Operations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance			(3)
Transfer to net assets held for sale			20
Other comprehensive income (loss) before reclassifications, after tax			2
Reclassification of (gains) losses from accumulated other comprehensive income, after tax			3
Other comprehensive income (loss)			5
Amounts attributable to noncontrolling interests			(1)
Ending, balance			21
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		(6)	(4)
Other comprehensive income (loss) before reclassifications, after tax		(2)	2
Reclassification of (gains) losses from accumulated other comprehensive income, after tax		5	1
Other comprehensive income (loss)		3	3
Amounts attributable to noncontrolling interests			(1)
Ending, balance	(3)	(3)	(2)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		(641)	(432)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax		4	(1)
Other comprehensive income (loss)		4	(1)
Issuance of equity securities by subsidiary		1
Amounts attributable to noncontrolling interests			1
Ending, balance	(636)	(636)	(432)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		49	133
Other comprehensive income (loss) before reclassifications, after tax		(96)	(6)
Other comprehensive income (loss)		(96)	(6)
Amounts attributable to noncontrolling interests		9
Ending, balance	$ (38)	$ (38)	$ 127