Stock-Based Compensation - Stock Options Outstanding and Exercisable (Detail) - 12 months ended Dec. 31, 2015 $ / shares in Units, $ in Millions	CAD / shares	USD ($) $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Number of options | shares		2,407,973
Options outstanding, Weighted average years to expiration	6 years 3 months 18 days
Options outstanding, Weighted average exercise price	CAD 113.01
Options outstanding, Aggregate intrinsic value | $		$ 153
Options exercisable, Number of options | shares		1,422,994
Options exercisable, Weighted average exercise price	CAD 80.55
Options outstanding, Aggregate intrinsic value | $		$ 137
Stock options in-the-money | shares		2,049,968
Stock options in-the-money weighted average exercise price | $ / shares		$ 93.81
Stock options weighted average contractual Term	5 years 3 months 18 days
Range of exercise prices from $36.29 - $72.54 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of option exercise prices, minimum	CAD 36.29
Range of option exercise prices, maximum	CAD 72.54
Options outstanding, Number of options | shares		464,345
Options outstanding, Weighted average years to expiration	2 years 9 months 22 days
Options outstanding, Weighted average exercise price	CAD 60.48
Options outstanding, Aggregate intrinsic value | $		$ 54
Options exercisable, Number of options | shares		464,345
Options exercisable, Weighted average exercise price	60.48
Options outstanding, Aggregate intrinsic value | $		$ 54
Range of exercise prices from $72.55 - $74.55 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of option exercise prices, minimum	72.55
Range of option exercise prices, maximum	CAD 74.55
Options outstanding, Number of options | shares		650,000
Options outstanding, Weighted average years to expiration	6 years 6 months 18 days
Options outstanding, Weighted average exercise price	CAD 73.39
Options outstanding, Aggregate intrinsic value | $		$ 67
Options exercisable, Number of options | shares		487,500
Options exercisable, Weighted average exercise price	73.39
Options outstanding, Aggregate intrinsic value | $		$ 50
Range of exercise prices from $74.56 - $129.15 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of option exercise prices, minimum	74.56
Range of option exercise prices, maximum	CAD 129.15
Options outstanding, Number of options | shares		644,608
Options outstanding, Weighted average years to expiration	6 years 6 months 18 days
Options outstanding, Weighted average exercise price	CAD 103.32
Options outstanding, Aggregate intrinsic value | $		$ 47
Options exercisable, Number of options | shares		394,104
Options exercisable, Weighted average exercise price	96.21
Options outstanding, Aggregate intrinsic value | $		$ 32
Range of exercise prices from $129.16 - $244.54 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of option exercise prices, minimum	129.16
Range of option exercise prices, maximum	CAD 244.54
Options outstanding, Number of options | shares		649,020
Options outstanding, Weighted average years to expiration	8 years 7 months 18 days
Options outstanding, Weighted average exercise price	CAD 199.89
Options outstanding, Aggregate intrinsic value | $		$ (15)
Options exercisable, Number of options | shares		77,045
Options exercisable, Weighted average exercise price	CAD 166.73
Options outstanding, Aggregate intrinsic value | $		$ 1