Investments in fixed maturity securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Summary of Investment Holdings [Line Items]
Amortized cost of fixed maturity securities	$ 27,214	$ 27,764
Unrealized gains on fixed maturity securities	1,827	1,752
Unrealized losses on fixed maturity securities	(90)	(146)
Fair value of fixed maturity securities	28,951	29,370
Carrying value of fixed maturity securities	28,953	29,353
Fixed Maturities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	26,546	27,085
Unrealized gains on available-for-sale securities	1,827	1,735
Unrealized losses on available-for-sale securities	(88)	(146)
Carrying value and fair value of available-for-sale securities	28,285	28,674
Fixed Maturities [Member] | Wm. Wrigley Jr. Company [Member]
Summary of Investment Holdings [Line Items]
Amortized cost and carrying value of held-to-maturity securities	668	679
Unrealized gains on held-to-maturity securities		17
Unrealized losses on held-to-maturity securities	(2)
Fair value of held-to-maturity securities	666	696
Fixed Maturities [Member] | U.S. Treasury, U.S. government corporations and agencies [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	2,831	2,650
Unrealized gains on available-for-sale securities	14	16
Unrealized losses on available-for-sale securities	(6)	(8)
Carrying value and fair value of available-for-sale securities	2,839	2,658
Fixed Maturities [Member] | States, municipalities and political subdivisions [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	1,923	2,221
Unrealized gains on available-for-sale securities	103	129
Unrealized losses on available-for-sale securities	(1)	(5)
Carrying value and fair value of available-for-sale securities	2,025	2,345
Fixed Maturities [Member] | Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	12,139	11,001
Unrealized gains on available-for-sale securities	265	182
Unrealized losses on available-for-sale securities	(74)	(110)
Carrying value and fair value of available-for-sale securities	12,330	11,073
Fixed Maturities [Member] | Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	8,030	9,383
Unrealized gains on available-for-sale securities	1,235	1,190
Unrealized losses on available-for-sale securities	(3)	(15)
Carrying value and fair value of available-for-sale securities	9,262	10,558
Fixed Maturities [Member] | Mortgage-backed securities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	1,623	1,830
Unrealized gains on available-for-sale securities	210	218
Unrealized losses on available-for-sale securities	(4)	(8)
Carrying value and fair value of available-for-sale securities	$ 1,829	$ 2,040