Derivative instruments (Cross-currency Swaps) (Details) - Jun. 30, 2015 - Cash flow hedge [Member] - Cross currency swap contracts [Member] € in Millions, £ in Millions, $ in Millions	USD ($)	EUR (€)	GBP (£)
2.125% euro denominated notes due 2019 (2.125% 2019 euro Notes) [Member]
Derivative [Line Items]
Notional amount	$ 864	€ 675
2.125% euro denominated notes due 2019 (2.125% 2019 euro Notes) [Member] | Interest rate received [Member]
Derivative [Line Items]
Interest rate	2.125%	2.125%	2.125%
2.125% euro denominated notes due 2019 (2.125% 2019 euro Notes) [Member] | Interest rate paid [Member]
Derivative [Line Items]
Interest rate	2.60%	2.60%	2.60%
5.50% pound sterling denominated notes due 2026 (5.50% 2026 pound sterling Notes) [Member]
Derivative [Line Items]
Notional amount	$ 747		£ 475
5.50% pound sterling denominated notes due 2026 (5.50% 2026 pound sterling Notes) [Member] | Interest rate received [Member]
Derivative [Line Items]
Interest rate	5.50%	5.50%	5.50%
5.50% pound sterling denominated notes due 2026 (5.50% 2026 pound sterling Notes) [Member] | Interest rate paid [Member]
Derivative [Line Items]
Interest rate	6.00%	6.00%	6.00%
4.00% pound sterling denominated notes due 2029 (4.00% 2029 pound sterling Notes) [Member]
Derivative [Line Items]
Notional amount	$ 1,111		£ 700
4.00% pound sterling denominated notes due 2029 (4.00% 2029 pound sterling Notes) [Member] | Interest rate received [Member]
Derivative [Line Items]
Interest rate	4.00%	4.00%	4.00%
4.00% pound sterling denominated notes due 2029 (4.00% 2029 pound sterling Notes) [Member] | Interest rate paid [Member]
Derivative [Line Items]
Interest rate	4.50%	4.50%	4.50%