Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance	$ 298	$ 563	$ 280	$ 339
Other comprehensive income (loss) before reclassifications, after tax	(288)	307	(268)	581
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	14	(36)	14	(60)
Other comprehensive income (loss)	(274)	271	(254)	521
Issuance of equity securities by subsidiary			1
Amounts attributable to noncontrolling interests	29	(27)	26	(53)
Ending, balance	53	807	53	807
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance	31	29	32	23
Transfer to net assets of discontinued operations				(5)
Other comprehensive income (loss) before reclassifications, after tax	(4)	2	(5)	14
Other comprehensive income (loss)	(4)	2	(5)	14
Amounts attributable to noncontrolling interests	1	(1)	1	(2)
Ending, balance	28	30	28	30
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance	944	820	846	622
Transfer to net assets of discontinued operations				(15)
Other comprehensive income (loss) before reclassifications, after tax	(370)	257	(251)	521
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	7	13	(2)	(14)
Other comprehensive income (loss)	(363)	270	(253)	507
Amounts attributable to noncontrolling interests	38	(28)	26	(52)
Ending, balance	619	1,062	619	1,062
Discontinued Operations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance		21		(3)
Transfer to net assets of discontinued operations				20
Other comprehensive income (loss) before reclassifications, after tax		3		5
Reclassification of (gains) losses from accumulated other comprehensive income, after tax		7		10
Other comprehensive income (loss)		10		15
Amounts attributable to noncontrolling interests		(1)		(2)
Ending, balance		30		30
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance	(3)	(2)	(6)	(4)
Other comprehensive income (loss) before reclassifications, after tax		3	(2)	5
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	1	(3)	6	(2)
Other comprehensive income (loss)	1		4	3
Amounts attributable to noncontrolling interests	(1)	(1)	(1)	(2)
Ending, balance	(3)	(3)	(3)	(3)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance	(636)	(432)	(641)	(432)
Other comprehensive income (loss) before reclassifications, after tax	37		37
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	6	(53)	10	(54)
Other comprehensive income (loss)	43	(53)	47	(54)
Issuance of equity securities by subsidiary			1
Amounts attributable to noncontrolling interests	(5)	7	(5)	8
Ending, balance	(598)	(478)	(598)	(478)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning, balance	(38)	127	49	133
Other comprehensive income (loss) before reclassifications, after tax	49	42	(47)	36
Other comprehensive income (loss)	49	42	(47)	36
Amounts attributable to noncontrolling interests	(4)	(3)	5	(3)
Ending, balance	$ 7	$ 166	$ 7	$ 166