Investments in fixed maturity securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Summary of Investment Holdings [Line Items]
Carrying value of fixed maturity securities	$ 29,558	$ 29,353
Fixed Maturities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	27,183	27,085
Unrealized gains on available-for-sale securities	1,819	1,735
Unrealized losses on available-for-sale securities	(104)	(146)
Carrying value and fair value of available-for-sale securities	28,898	28,674
Amortized cost of fixed maturity securities	27,843	27,764
Unrealized gains on fixed maturity securities	1,833	1,752
Unrealized losses on fixed maturity securities	(104)	(146)
Fair value of fixed maturity securities	29,572	29,370
Carrying value of fixed maturity securities	29,558	29,353
Fixed Maturities [Member] | Wm. Wrigley Jr. Company [Member]
Summary of Investment Holdings [Line Items]
Amortized cost and carrying value of held-to-maturity securities	660	679
Unrealized gains on held-to-maturity securities	14	17
Fair value of held-to-maturity securities	674	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	2,926	2,650
Unrealized gains on available-for-sale securities	16	16
Unrealized losses on available-for-sale securities	(7)	(8)
Carrying value and fair value of available-for-sale securities	2,935	2,658
Fixed Maturities [Member] | States, municipalities and political subdivisions [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	2,074	2,221
Unrealized gains on available-for-sale securities	113	129
Unrealized losses on available-for-sale securities	(2)	(5)
Carrying value and fair value of available-for-sale securities	2,185	2,345
Fixed Maturities [Member] | Foreign governments [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	12,201	11,001
Unrealized gains on available-for-sale securities	221	182
Unrealized losses on available-for-sale securities	(85)	(110)
Carrying value and fair value of available-for-sale securities	12,337	11,073
Fixed Maturities [Member] | Corporate bonds [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	8,213	9,383
Unrealized gains on available-for-sale securities	1,245	1,190
Unrealized losses on available-for-sale securities	(4)	(15)
Carrying value and fair value of available-for-sale securities	9,454	10,558
Fixed Maturities [Member] | Mortgage-backed securities [Member]
Summary of Investment Holdings [Line Items]
Amortized cost of available-for-sale securities	1,769	1,830
Unrealized gains on available-for-sale securities	224	218
Unrealized losses on available-for-sale securities	(6)	(8)
Carrying value and fair value of available-for-sale securities	$ 1,987	$ 2,040