Incentive Plans - Schedule of Activity Relating to RSUs and DSUs (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units, Beginning Balance	13,529,116	16,630,009	21,481,131
Units, Granted	4,296,386	3,825,737	5,186,627
Units, Forfeited	(469,776)	(344,345)	(268,900)
Units, Vested	(7,756,068)	(6,582,285)	(9,768,849)
Units, Ending Balance	9,599,658	13,529,116	16,630,009
Weighted Average Grant Date Fair Value, Beginning Balance	$ 35.19	$ 34.51	$ 33.92
Weighted Average Grant Date Fair Value, Granted	48.57	42.59	37.21
Weighted Average Grant Date Fair Value, Forfeited	43.54	34.52	34.47
Weighted Average Grant Date Fair Value, Vested	31.12	37.80	34.65
Weighted Average Grant Date Fair Value, Ending Balance	$ 44.06	$ 35.19	$ 34.51
DSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units, Beginning Balance	286,227	251,434	204,496
Units, Granted	26,443	34,793	46,938
Units, Ending Balance	312,670	286,227	251,434
Weighted Average Grant Date Fair Value, Beginning Balance	$ 34.21	$ 32.02	$ 31.47
Weighted Average Grant Date Fair Value, Granted	55.11	50.04	34.42
Weighted Average Grant Date Fair Value, Ending Balance	$ 35.98	$ 34.21	$ 32.02