Other investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	$ 13,111	$ 19,333
Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	3,810	3,676
Other Fixed Maturity and Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost	16,249	18,442
Net Unrealized Gains	1,678	5,705
Fair Value	17,927	24,147
Carrying Value	16,921	23,009
Other Fixed Maturity and Equity Securities [Member] | Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Cost	13,051	15,700
Net Unrealized Gains	1,055	4,758
Fair Value	14,106	20,458
Carrying Value	13,111	19,333
Other Fixed Maturity and Equity Securities [Member] | Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Cost	3,198	2,742
Net Unrealized Gains	623	947
Fair Value	3,821	3,689
Carrying Value	$ 3,810	$ 3,676