Earnings per Share - Basic and Diluted Earnings Per Unit (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allocation of net income among partner interests [Abstract]
Net income attributable to common unitholders	$ 175.6	$ 179.2	$ 274.3	$ 279.1
Denominator - basic and diluted partnership units:
Total weighted average basic and diluted units outstanding (shares)	428.9	429.2	428.9	430.5
Class A common units
Allocation of net income among partner interests [Abstract]
Net income attributable to common unitholders	$ 89.5	$ 90.9	$ 139.7	$ 140.9
Denominator - basic and diluted partnership units:
Total weighted average basic and diluted units outstanding (shares)	202.0	202.0	202.0	202.0
Earnings per unit - basic and diluted:
Earnings per unit / share - basic and diluted (in dollars per share)	$ 0.44	$ 0.45	$ 0.69	$ 0.70
Partnership exchangeable units
Allocation of net income among partner interests [Abstract]
Net income attributable to common unitholders	$ 86.1	$ 88.3	$ 134.6	$ 138.2
Denominator - basic and diluted partnership units:
Total weighted average basic and diluted units outstanding (shares)	226.9	227.2	226.9	228.5
Earnings per unit - basic and diluted:
Earnings per unit / share - basic and diluted (in dollars per share)	$ 0.38	$ 0.39	$ 0.59	$ 0.60