Other investments - Narrative (Detail) (USD $)							3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended		12 Months Ended
	Mar. 31, 2014 Finance and Financial Products [Member]	Dec. 31, 2013 Finance and Financial Products [Member]	Mar. 31, 2014 Insurance and Other [Member]	Dec. 31, 2013 Insurance and Other [Member]	Mar. 31, 2014 Other Equity Securities [Member] Available-for-sale Securities [Member]	Dec. 31, 2013 Other Equity Securities [Member] Available-for-sale Securities [Member]	Mar. 31, 2014 Wm. Wrigley Jr. Company [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Finance and Financial Products [Member]	Mar. 31, 2014 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]	Mar. 31, 2014 Bank of America Corporation [Member] Other Equity Securities [Member] Available-for-sale Securities [Member] Cumulative 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]	Mar. 31, 2014 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]	Mar. 31, 2014 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]	Mar. 31, 2014 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									3,000,000,000				5,000,000,000
Conversion ratio of preferred stock into common stock								24.201
Preferred stock conversion price, per share								$ 41.32
Common stock threshold price, per share, to trigger the issuer's option to convert preferred stock into common stock								$ 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	$ 5,884,000,000	$ 5,617,000,000	$ 13,259,000,000	$ 12,334,000,000	$ 19,143,000,000	$ 17,951,000,000