Investment gains/losses and other-than-temporary impairment losses on investments - Narrative (Detail) (USD $) Share data in Millions, unless otherwise specified	6 Months Ended					3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Fixed Maturities [Member]	Dec. 31, 2011 Fixed Maturities [Member]	Mar. 31, 2012 Fixed Maturities [Member] Texas Competitive Electric Holdings [Member]	Jun. 30, 2011 Other Fixed Maturity and Equity Securities [Member] Goldman Sachs Group Inc [Member] Cumulative Perpetual Preferred Stock [Member]	Mar. 31, 2011 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]
Investment and other gains / losses [Line Items]
Realized gain from redemption of securities							$ 1,250,000,000
Other-than-temporary impairment of securities	337,000,000	506,000,000				337,000,000		506,000,000	337,000,000
Number of shares in loss position before OTTI adjustment									103.6
Cost of investment in loss position before OTTI adjustment									3,621,000,000
Number of shares in gain position									255.4
Cost of investment in gain position	51,194,000,000		49,610,000,000						4,394,000,000
Gross unrealized gains	$ 35,710,000,000		$ 28,773,000,000	$ 2,712,000,000	$ 2,358,000,000				$ 3,704,000,000