Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 22,810	$ 24,650
Other comprehensive income (loss) before reclassifications, after tax	$ 273	$ (288)	507	(268)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	4	14	26	14
Other comprehensive income (loss)	277	(274)	533	(254)
Issuance of equity securities by subsidiary				1
Amounts attributable to noncontrolling interests	(32)	29	(57)	26
Ending Balance	23,031	24,332	23,031	24,332
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	29	31	24	32
Other comprehensive income (loss) before reclassifications, after tax	(1)	(4)	2	(5)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax			2
Other comprehensive income (loss)	(1)	(4)	4	(5)
Amounts attributable to noncontrolling interests		1		1
Ending Balance	28	28	28	28
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	554	944	347	846
Other comprehensive income (loss) before reclassifications, after tax	322	(370)	539	(251)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	(1)	7	10	(2)
Other comprehensive income (loss)	321	(363)	549	(253)
Amounts attributable to noncontrolling interests	(37)	38	(58)	26
Ending Balance	838	619	838	619
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2)	(3)	(3)	(6)
Other comprehensive income (loss) before reclassifications, after tax				(2)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax		1	1	6
Other comprehensive income (loss)		1	1	4
Amounts attributable to noncontrolling interests		(1)		(1)
Ending Balance	(2)	(3)	(2)	(3)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(643)	(636)	(649)	(641)
Other comprehensive income (loss) before reclassifications, after tax		37		37
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	5	6	13	10
Other comprehensive income (loss)	5	43	13	47
Issuance of equity securities by subsidiary				1
Amounts attributable to noncontrolling interests	(1)	(5)	(3)	(5)
Ending Balance	(639)	(598)	(639)	(598)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(64)	(38)	(76)	49
Other comprehensive income (loss) before reclassifications, after tax	(48)	49	(34)	(47)
Other comprehensive income (loss)	(48)	49	(34)	(47)
Amounts attributable to noncontrolling interests	6	(4)	4	5
Ending Balance	(106)	7	(106)	7
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(126)	298	(357)	280
Other comprehensive income (loss)			476	(228)
Ending Balance	$ 119	$ 53	$ 119	$ 53