Other investments - Narrative (Detail) (USD $)	12 Months Ended								72 Months Ended	12 Months Ended		60 Months Ended	12 Months Ended	36 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2013 Finance and Financial Products [Member]	Dec. 31, 2012 Finance and Financial Products [Member]	Dec. 31, 2013 Insurance and Other [Member]	Dec. 31, 2012 Insurance and Other [Member]	Dec. 31, 2013 Other Equity Securities [Member] Available-for-sale Securities [Member]	Dec. 31, 2012 Other Equity Securities [Member] Available-for-sale Securities [Member]	Dec. 31, 2013 Wm Wrigley Jr Company [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Finance and Financial Products [Member]	Dec. 31, 2013 The Dow Chemical Company [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Insurance and Other [Member] Series A Cumulative Convertible Perpetual Preferred Stock [Member]	Dec. 31, 2009 The Dow Chemical Company [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Insurance and Other [Member] Series A Cumulative Convertible Perpetual Preferred Stock [Member]	Dec. 31, 2013 The Dow Chemical Company [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Insurance and Other [Member] Series A Cumulative Convertible Perpetual Preferred Stock [Member]	Dec. 31, 2011 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2013 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Cumulative Perpetual Preferred Stock [Member]	Dec. 31, 2013 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Warrants Expiring 2021 [Member]	Dec. 31, 2011 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Cumulative Perpetual Preferred Stock and Warrants [Member]	Dec. 31, 2011 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Finance and Financial Products [Member] Cumulative Perpetual Preferred Stock and Warrants [Member]	Dec. 31, 2011 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Insurance and Other [Member] Cumulative Perpetual Preferred Stock and Warrants [Member]
Other Investments [Line Items]
Investment in preferred stock, liquidation value									$ 2,100,000,000
Investment in preferred stock, stated dividend rate									5.00%			8.50%		6.00%
Investment, number of shares purchased											3,000,000		50,000
Amount paid for an investment	12,250,000,000	5,000,000,000									3,000,000,000					5,000,000,000
Conversion ratio of preferred stock into common stock										24.201		24.201
Preferred stock conversion price, per share										$ 41.32		$ 41.32
Common stock threshold price, per share, to trigger the issuer's option to convert preferred stock into common stock										$ 53.72		$ 53.72
Minimum number of trading days in a consecutive-day period that the issuer's common stock price must exceed to trigger the issuer's option to convert preferred stock to common stock										20 days
Range of trading days in a consecutive day period, number of days										30 days
Number of common shares that can be purchased															700,000,000
Redemption value of Cumulative Perpetual Preferred Stock, per share														$ 105,000
Redemption value of Cumulative Perpetual Preferred Stock, aggregate value														5,250,000,000
Aggregate cost to exercise warrants															5,000,000,000
Exercise price for warrants, per share															$ 7.142857
Investment allocation percentage																	20.00%	80.00%
Other investments, cost basis							10,000,000,000
Other investments, fair value			$ 5,617,000,000	$ 4,882,000,000	$ 12,334,000,000	$ 10,184,000,000	$ 17,951,000,000	$ 15,066,000,000