Other investments - Narrative (Detail) - Available-for-sale Securities [Member] - USD ($)		9 Months Ended	12 Months Ended
	Sep. 27, 2016	Sep. 30, 2016	Dec. 31, 2008
Wm. Wrigley Jr. Company [Member]
Other Investments [Line Items]
Percentage of original preferred stock investment expected to be redeemed or called		50.00%
Preferred stock redemption period		90 days
Preferred stock redemption period start date		Oct. 06, 2016
Wm. Wrigley Jr. Company [Member] | Preferred Stock [Member]
Other Investments [Line Items]
Purchase of investment			$ 2,100,000,000
Sale of investment	$ 4,560,000,000
Series A Cumulative Convertible Perpetual Preferred Stock [Member] | The Dow Chemical Company [Member]
Other Investments [Line Items]
Investment, number of shares owned		3,000,000
Investment in preferred stock, liquidation value per share		$ 1,000
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
Investment in preferred stock, stated dividend rate		8.50%
Non-Cumulative Perpetual Preferred Stock [Member] | Bank of America Corporation [Member]
Other Investments [Line Items]
Preferred stock redemption period start date		May 07, 2019
Investment, number of shares owned		50,000
Investment in preferred stock, liquidation value per share		$ 100,000
Investment in preferred stock, stated dividend rate		6.00%
Redemption value of Perpetual Preferred Stock, per share		$ 105,000
Redemption value of Perpetual Preferred Stock, aggregate value		$ 5,250,000,000
Warrants Expiring 2021 [Member] | Bank of America Corporation [Member]
Other Investments [Line Items]
Number of common shares that can be purchased		700,000,000
Aggregate cost to exercise warrants		$ 5,000,000,000
Exercise price for warrants, per share		$ 7.142857
Class A 9% Cumulative Compounding Perpetual Preferred Stock [Member] | RBI [Member]
Other Investments [Line Items]
Preferred stock redemption period start date		Dec. 12, 2017
Investment in preferred stock, stated dividend rate		9.00%
Stated value of equity securities		$ 3,000,000,000
Preferred stock redemption at option of holder start date		Dec. 12, 2024
Preferred stock redemption price percentage		109.90%