Acquisitions - Pro-Forma Information (Details) - HPES - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Revenues	$ 4,380		$ 8,708
Net income	$ 455		$ 645
Business Acquisition, Pro Forma Information [Abstract]
Revenues		$ 6,355		$ 12,773
Net income (loss)		(123)		(404)
Loss attributable to the Company		$ (130)		$ (413)
Loss per common share:
Loss per common share, Basic (in dollars per share)		$ (0.46)		$ (1.46)
Loss per common share, Diluted (in dollars per share)		$ (0.46)		$ (1.46)