Other investments - Narrative (Detail) (Available-for-sale Securities [Member], USD $) In Billions, except Share data, unless otherwise specified	12 Months Ended			1 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2014	Dec. 12, 2014
The Dow Chemical Company [Member] | Series A Cumulative Convertible Perpetual Preferred Stock [Member]
Other Investments [Line Items]
Investment in preferred stock, stated dividend rate	8.50%
Investment, number of shares purchased		3,000,000
Amount paid for an investment		$ 3
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
Bank of America Corporation [Member] | Cumulative Perpetual Preferred Stock [Member]
Other Investments [Line Items]
Investment in preferred stock, stated dividend rate	6.00%
Investment, number of shares purchased			50,000
Redemption value of Perpetual Preferred Stock, per share	$ 105,000			$ 105,000
Redemption value of Perpetual Preferred Stock, aggregate value	5.25			5.25
Bank of America Corporation [Member] | Warrants Expiring 2021 [Member]
Other Investments [Line Items]
Number of common shares that can be purchased	700,000,000			700,000,000
Aggregate cost to exercise warrants	5			5
Exercise price for warrants, per share	$ 7.142857
Bank of America Corporation [Member] | Cumulative Perpetual Preferred Stock and Warrants [Member]
Other Investments [Line Items]
Amount paid for an investment			5
Wm. Wrigley Jr. Company [Member]
Other Investments [Line Items]
Investment in preferred stock, liquidation value	2.1			2.1
Investment in preferred stock, stated dividend rate	5.00%
RBI - Parent Company of Burger King and Tim Hortons [Member] | Class A 9% Cumulative Compounding Perpetual Preferred Stock [Member]
Other Investments [Line Items]
Investment in preferred stock, stated dividend rate				9.00%
Stated value of equity securities acquired					3
RBI - Parent Company of Burger King and Tim Hortons [Member] | Class A 9% Cumulative Compounding Perpetual Preferred Stock and Common Stock [Member]
Other Investments [Line Items]
Amount paid for an investment					$ 3
Percentage of voting interests					14.40%