CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Payments for deepwater rig exit costs			$ 266.6
Cost of acquired assets, cash paid	$ 206.7
Minimum [Member]
Maturity of Canadian government securities		90 days	90 days	90 days