Investments in fixed maturity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 23,283	$ 25,049
Unrealized gains on fixed maturity securities	1,399	1,107
Unrealized losses on fixed maturity securities	(35)	(129)
Fair value of fixed maturity securities	24,647	26,027
U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	4,549	3,425
Unrealized gains on fixed maturity securities	17	10
Unrealized losses on fixed maturity securities	(1)	(8)
Fair value of fixed maturity securities	4,565	3,427
States, municipalities and political subdivisions [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,216	1,695
Unrealized gains on fixed maturity securities	64	71
Unrealized losses on fixed maturity securities	(1)	(2)
Fair value of fixed maturity securities	1,279	1,764
Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	9,454	11,327
Unrealized gains on fixed maturity securities	362	226
Unrealized losses on fixed maturity securities	(21)	(85)
Fair value of fixed maturity securities	9,795	11,468
Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	6,996	7,323
Unrealized gains on fixed maturity securities	800	632
Unrealized losses on fixed maturity securities	(7)	(29)
Fair value of fixed maturity securities	7,789	7,926
Mortgage-backed securities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	1,068	1,279
Unrealized gains on fixed maturity securities	156	168
Unrealized losses on fixed maturity securities	(5)	(5)
Fair value of fixed maturity securities	$ 1,219	$ 1,442

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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