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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 (€)
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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% |  |  |  |  |

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- Definition Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13,16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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