Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Dividends [Abstract]
Total dividends per share for the period (in USD per share)	$ 1.449	$ 1.441	$ 1.433
Total dividend payments	$ 337.5	$ 315.4	$ 291.1

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Name:	us-gaap_DividendsCommonStockCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration