Share Transactions - Share-based compensation (Details) - $ / shares	3 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted in period, shares	2,199,656	1,477,398
Options granted - Weighted average grant date fair value, per share	$ 7.43	$ 8.22
Restricted shares and units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards other than options granted in period, shares	1,264,931	1,534,908
Awards other than options granted - Weighted average grant date fair value, per share	$ 26.56	$ 32.09
Performance shares and units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards other than options granted in period, shares	705,345
Awards other than options granted - Weighted average grant date fair value, per share	$ 24.65

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Gross number of share options (or share units) granted during the period.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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