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Debt - Summary of outstanding debt (Details) | Dec. 31, 2017 USD ($) | Dec. 31, 2017 EUR (€) | Dec. 31, 2017 CAD | Dec. 31, 2016 USD ($) | Mar. 01, 2016 USD ($)
--- | --- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 5,966,000,000 |  |  | $ 6,205,000,000 |
Less: Short-term and current portion of long-term debt | 299,000,000 |  |  | 336,000,000 |
Long-term debt | 5,667,000,000 |  |  | 5,869,000,000 |
Commercial Paper |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | 0 |  |  | 329,000,000 |
Other |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | 3,000,000 |  |  | 9,000,000 |
3.875% Senior Notes due December 2025 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 745,000,000 |  |  | 744,000,000 |
Interest rate on debt | 3.875% | 3.875% | 3.875% |  |
Debt face value |  |  |  |  | $ 750,000,000
5.00% Senior Notes due September 2020 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 598,000,000 |  |  | 598,000,000 |
Interest rate on debt | 5.00% | 5.00% | 5.00% |  |
3.50% Senior Notes due June 2024 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 592,000,000 |  |  | 594,000,000 |
Interest rate on debt | 3.50% | 3.50% | 3.50% |  |
4.75% Senior Notes due May 2045 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 595,000,000 |  |  | 592,000,000 |
Interest rate on debt | 4.75% | 4.75% | 4.75% |  |
2.875% Senior Notes due May 2026 (EUR 500M) | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 544,000,000 |  |  | 516,000,000 |
Interest rate on debt | 2.875% | 2.875% | 2.875% |  |
Debt face value | € |  | € 500,000,000 |  |  |
4.60% Senior Notes due June 2044 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 587,000,000 |  |  | 543,000,000 |
Interest rate on debt | 4.60% | 4.60% | 4.60% |  |
8.205% Junior Subordinated Notes due January 2027 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 521,000,000 |  |  | 521,000,000 |
Interest rate on debt | 8.205% | 8.205% | 8.205% |  |
2.80% Senior Notes due March 2021 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 398,000,000 |  |  | 397,000,000 |
Interest rate on debt | 2.80% | 2.80% | 2.80% |  |
4.00% Senior Notes due November 2023 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 348,000,000 |  |  | 347,000,000 |
Interest rate on debt | 4.00% | 4.00% | 4.00% |  |
6.25% Senior Notes due September 2040 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 296,000,000 |  |  | 295,000,000 |
Interest rate on debt | 6.25% | 6.25% | 6.25% |  |
4.76% Senior Notes due March 2018 (CAD 375M) | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 296,000,000 |  |  | 277,000,000 |
Interest rate on debt | 4.76% | 4.76% | 4.76% |  |
Debt face value | CAD |  |  | CAD 375,000,000 |  |
4.45% Senior Notes due May 2043 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 246,000,000 |  |  | 246,000,000 |
Interest rate on debt | 4.45% | 4.45% | 4.45% |  |
4.25% Senior Notes due December 2042 | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Total debt | $ 197,000,000 |  |  | $ 197,000,000 |
Interest rate on debt | 4.25% | 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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