Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 22,810	$ 24,650	$ 24,906
Other comprehensive income (loss) before reclassifications, after tax	156	(795)	(28)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	(3)	77	(41)
Other comprehensive income (loss)	153	(718)	(69)
Issuance of equity securities by subsidiary		1
Amounts attributable to noncontrolling interests	(19)	80	10
Ending Balance	23,361	22,810	24,650
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	24	32	23
Sale of subsidiaries			(5)
Other comprehensive income (loss) before reclassifications, after tax	9	(23)	15
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	(6)	14
Other comprehensive income (loss)	3	(9)	15
Amounts attributable to noncontrolling interests		1	(1)
Ending Balance	27	24	32
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	347	846	622
Sale of subsidiaries			(15)
Other comprehensive income (loss) before reclassifications, after tax	283	(600)	295
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	(26)	43	(28)
Other comprehensive income (loss)	257	(557)	267
Amounts attributable to noncontrolling interests	(28)	58	(28)
Ending Balance	576	347	846
Discontinued Operations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(3)
Sale of subsidiaries			20
Other comprehensive income (loss) before reclassifications, after tax			2
Reclassification of (gains) losses from accumulated other comprehensive income, after tax			(21)
Other comprehensive income (loss)			(19)
Amounts attributable to noncontrolling interests			2
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3)	(6)	(4)
Other comprehensive income (loss) before reclassifications, after tax		(2)	(2)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	2	7	(1)
Other comprehensive income (loss)	2	5	(3)
Amounts attributable to noncontrolling interests	(1)	(2)	1
Ending Balance	(2)	(3)	(6)
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(649)	(641)	(432)
Other comprehensive income (loss) before reclassifications, after tax	(22)	(31)	(244)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	27	13	9
Other comprehensive income (loss)	5	(18)	(235)
Issuance of equity securities by subsidiary		1
Amounts attributable to noncontrolling interests	(2)	9	26
Ending Balance	(646)	(649)	(641)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(76)	49	133
Other comprehensive income (loss) before reclassifications, after tax	(114)	(139)	(94)
Other comprehensive income (loss)	(114)	(139)	(94)
Amounts attributable to noncontrolling interests	12	14	10
Ending Balance	(178)	(76)	49
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(357)	280	339
Other comprehensive income (loss)	134	(638)	(59)
Ending Balance	$ (223)	$ (357)	$ 280