Other investments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	$ 16,779	$ 16,057
Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Carrying Value	5,152	4,952
Other Fixed Maturity and Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Cost	16,779	16,257
Net Unrealized Gains	5,982	5,627
Fair Value	22,761	21,884
Carrying Value	21,931	21,009
Other Fixed Maturity and Equity Securities [Member] | Insurance and Other [Member]
Summary of Investment Holdings [Line Items]
Cost	13,561	13,109
Net Unrealized Gains	4,048	3,823
Fair Value	17,609	16,932
Carrying Value	16,779	16,057
Other Fixed Maturity and Equity Securities [Member] | Finance and Financial Products [Member]
Summary of Investment Holdings [Line Items]
Cost	3,218	3,148
Net Unrealized Gains	1,934	1,804
Fair Value	5,152	4,952
Carrying Value	$ 5,152	$ 4,952