Other investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	$ 16,057	$ 13,111
Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	4,952	3,810
Other Fixed Maturity and Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost	16,257	16,249
Net Unrealized Gains	5,627	1,678
Fair Value	21,884	17,927
Carrying Value	21,009	16,921
Other Fixed Maturity and Equity Securities [Member] | Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Cost	13,109	13,051
Net Unrealized Gains	3,823	1,055
Fair Value	16,932	14,106
Carrying Value	16,057	13,111
Other Fixed Maturity and Equity Securities [Member] | Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Cost	3,148	3,198
Net Unrealized Gains	1,804	623
Fair Value	4,952	3,821
Carrying Value	$ 4,952	$ 3,810