Employee Benefits - Employee Benefit Costs (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Defined Benefit Plans [Abstract]
Stock compensation expense	$ 13	$ 17	$ 1
Reversal of stock compensation cost	$ 5

The amount of expense from share-based payment transactions with employees.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_ExpenseFromSharebasedPaymentTransactionsWithEmployees
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration