Segment Information (Adjusted Share-Based Compensation Expense) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Share-based compensation expense		$ 23.6	$ 24.0	$ 47.4	$ 46.2
Adjusted share-based compensation expense		23.6	14.9	47.4	28.5
Corporate and reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Adjusted share-based compensation expense	[1]	23.6	14.9	47.4	28.5
General and administrative expense
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Share-based compensation expense		23.2	21.6	46.5	43.8
General and administrative expense | Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Bonus related share-based compensation included in segment and corporate general and administrative expense		0.0	(6.7)	0.0	(15.3)
Restructuring and other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Share-based compensation expense		0.0	2.4	0.0	2.4
Restructuring and other | Corporate and reconciling items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Bonus related share-based compensation included in segment and corporate general and administrative expense		$ 0.0	$ (2.4)	$ 0.0	$ (2.4)

[1] The following table reconciles total share-based compensation expense to adjusted share-based compensation expense: Three Months Ended Six Months Ended September 30, September 30, 2017 2016 2017 2016 (Amounts in millions)Total share-based compensation expense$23.6 $24.0 $47.4 $46.2Less: Bonus related share-based compensation included in segment and corporate general and administrative expense(i)— (6.7) — (15.3)Amount included in restructuring and other(ii)— (2.4) — (2.4)Adjusted share-based compensation$23.6 $14.9 $47.4 $28.5(i)Represents immediately vested stock awards granted as part of our annual bonus program issued in lieu of cash bonuses, which are, when granted, included in segment or corporate general and administrative expense.(ii)Represents share-based compensation expense included in restructuring and other expenses reflecting the impact of the acceleration of certain vesting schedules for equity awards pursuant to certain severance arrangements.