Investment gains/losses and other-than-temporary impairment losses - Narrative (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended							3 Months Ended			12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Equity Securities and Other Investments [Member]	Dec. 31, 2010 Equity Securities and Other Investments [Member]	Dec. 31, 2009 Equity Securities and Other Investments [Member]	Dec. 31, 2011 Equity Securities and Other Investments [Member] Cumulative Perpetual Preferred Stock [Member]	Mar. 31, 2011 Equity Securities and Other Investments [Member] Equity Securities [Member]	Dec. 31, 2010 Equity Securities and Other Investments [Member] Equity Securities [Member]	Mar. 31, 2011 Equity Securities and Other Investments [Member] Equity Securities [Member] Wells Fargo and Company [Member]	Dec. 31, 2010 Capital Instrument [Member] Swiss Reinsurance Company Limited [Member]	Dec. 31, 2010 Fixed Maturities [Member]	Dec. 31, 2011 Fixed Maturities [Member]	Dec. 31, 2010 Fixed Maturities [Member]	Dec. 31, 2009 Fixed Maturities [Member]	Dec. 31, 2010 BNSF [Member] Other Investment Gains / Losses [Member]
Investment and other gains / losses [Line Items]
Gains from sales and other disposals				$ 1,889	$ 2,603	$ 701	$ 1,775				$ 1,300		$ 310	$ 720	$ 357
One-time holding gain related to business acquisition		979														979
Other-than-temporary impairment of securities	908	1,973	3,155					506	938	337		1,020
Number of shares in loss position before OTTI adjustment										103.6
Individual impairment loss as a percent of the original cost									20.00%
Cost of investment in loss position before OTTI adjustment										3,621
Number of shares in gain position										255.4
Cost of investment in gain position	49,610	35,544								4,394
Gross unrealized gains	$ 28,773	$ 26,641								$ 3,704