Shareholders' equity and share-based payments - Share cancellation (Details)		12 Months Ended
Dec. 15, 2016 subsidiary shares	Dec. 31, 2016 shares
Subsidiaries from which cancelled treasury shares were previously bought back
Shareholders' equity
Number of indirectly controlled subsidiaries \| subsidiary	4
Cumulative percentage of interest held	100.00%
Treasury shares
Shareholders' equity
Cancellation of treasury shares \| shares	100,331,268	100,331,268

The proportion of ownership interest in a subsidiary attributable to the entity. [Refer: Subsidiaries [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 27
-IssueDate 2017-01-01
-Paragraph 17
-Subparagraph b
-Clause iii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_17_b_iii&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 27
-IssueDate 2017-01-01
-Paragraph 16
-Subparagraph b
-Clause iii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_16_b_iii&doctype=Standard
-URIDate 2017-03-09

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2017-01-01
-Paragraph 19B
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_19B_c&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_ProportionOfOwnershipInterestInSubsidiary
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration