Other investments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	$ 14,980	$ 13,111
Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	4,719	3,810
Other Fixed Maturity and Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost	16,252	16,249
Net Unrealized Gains	4,382	1,678
Fair Value	20,634	17,927
Carrying Value	19,699	16,921
Other Fixed Maturity and Equity Securities [Member] | Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Cost	13,054	13,051
Net Unrealized Gains	2,851	1,055
Fair Value	15,905	14,106
Carrying Value	14,980	13,111
Other Fixed Maturity and Equity Securities [Member] | Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Cost	3,198	3,198
Net Unrealized Gains	1,531	623
Fair Value	4,729	3,821
Carrying Value	$ 4,719	$ 3,810