Debt - Summary of outstanding debt (Details)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 CAD	Nov. 13, 2015 USD ($)	May. 20, 2015 USD ($)	Dec. 31, 2014 USD ($)	May. 20, 2014 USD ($)	May. 07, 2014 EUR (€)
Debt Instrument [Line Items]
Total debt	$ 5,737,000,000				$ 5,582,000,000
Less short-term and current portion of long-term debt	562,000,000				783,000,000
Long-term debt	5,175,000,000				4,799,000,000
Commercial Paper [Member]
Debt Instrument [Line Items]
Total debt	50,000,000				168,000,000
Other [Member]
Debt Instrument [Line Items]
Total debt	16,000,000				31,000,000
2.80% Senior Notes due 2021 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 399,000,000				0
Interest rate on debt ( in percentage)	2.80%	2.80%
Debt face value			$ 400,000,000
4.75% Senior Notes due 2045 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 598,000,000				0
Interest rate on debt ( in percentage)	4.75%	4.75%
Debt face value				$ 600,000,000
3.50% Senior Notes due June 2024 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 597,000,000				597,000,000
Interest rate on debt ( in percentage)	3.50%	3.50%
4.76% Senior Notes due March 2018 (CAD 375M) | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 271,000,000				322,000,000
Interest rate on debt ( in percentage)	4.76%	4.76%
Debt face value | CAD		CAD 375,000,000
4.45% Senior Notes due May 2043 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 249,000,000				248,000,000
Interest rate on debt ( in percentage)	4.45%	4.45%
2.875% Senior Notes due May 2026 (EUR 500M) | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 545,000,000				605,000,000
Interest rate on debt ( in percentage)	2.875%	2.875%
Debt face value	$ 500,000,000
2.875% Senior Notes due May 2026 (EUR 500M) | Other [Member]
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)							2.875%
Debt face value | €							€ 500,000,000
3.50% Senior Notes due September 2015 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 0				599,000,000
Interest rate on debt ( in percentage)	3.50%	3.50%
5.00% Senior Notes due September 2020 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 599,000,000				599,000,000
Interest rate on debt ( in percentage)	5.00%	5.00%
4.60% Senior Notes due June 2044 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 549,000,000				549,000,000
Interest rate on debt ( in percentage)	4.60%	4.60%
4.60% Senior Notes due June 2044 | Other [Member]
Debt Instrument [Line Items]
Interest rate on debt ( in percentage)						4.60%
Debt face value						$ 550,000,000
8.205% Junior Subordinated Notes due January 2027 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 521,000,000				521,000,000
Interest rate on debt ( in percentage)	8.205%	8.205%
3.125% Senior Notes due May 2016 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 500,000,000				500,000,000
Interest rate on debt ( in percentage)	3.125%	3.125%
Debt face value	$ 500,000,000
4.00% Senior Notes due November 2023 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 349,000,000				349,000,000
Interest rate on debt ( in percentage)	4.00%	4.00%
6.25% Senior Notes due September 2040 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 298,000,000				298,000,000
Interest rate on debt ( in percentage)	6.25%	6.25%
4.25% Senior Notes due December 2042 | Senior Notes [Member]
Debt Instrument [Line Items]
Total debt	$ 196,000,000				$ 196,000,000
Interest rate on debt ( in percentage)	4.25%	4.25%