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Debt - Narrative (Details) |  | 3 Months Ended | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
May. 07, 2014 EUR (€) | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($) credit_facility | Dec. 31, 2014 USD ($) | Dec. 31, 2015 CAD credit_facility | Dec. 31, 2015 EUR (€) credit_facility | Nov. 13, 2015 USD ($) | May. 20, 2015 USD ($) | Feb. 01, 2015 EUR (€) | Aug. 12, 2014 USD ($) | May. 20, 2014 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of credit facilities | credit_facility |  |  | 2 |  | 2 | 2 |  |  |  |  |
Total debt |  |  | $ 5,737,000,000 | $ 5,582,000,000 |  |  |  |  |  |  |
Weighted average commercial paper outstanding |  |  | $ 402,000,000 | 308,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 4.76% Senior Notes due March 2018 (CAD 375M) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value | CAD |  |  |  |  | CAD 375,000,000 |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 4.76% |  | 4.76% | 4.76% |  |  |  |  |
Total debt |  |  | $ 271,000,000 | 322,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 5.00% Senior Notes due September 2020 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 5.00% |  | 5.00% | 5.00% |  |  |  |  |
Total debt |  |  | $ 599,000,000 | 599,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 6.25% Senior Notes due September 2040 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 6.25% |  | 6.25% | 6.25% |  |  |  |  |
Total debt |  |  | $ 298,000,000 | 298,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 3.125% Senior Notes due May 2016 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value |  |  | $ 500,000,000 |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 3.125% |  | 3.125% | 3.125% |  |  |  |  |
Total debt |  |  | $ 500,000,000 | 500,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 4.75% Senior Notes due 2045 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value |  |  |  |  |  |  |  | $ 600,000,000 |  |  |
Interest rate on debt ( in percentage) |  |  | 4.75% |  | 4.75% | 4.75% |  |  |  |  |
Total debt |  |  | $ 598,000,000 | 0 |  |  |  |  |  |  |
Senior Notes [Member] | 2.80% Senior Notes due 2021 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value |  |  |  |  |  |  | $ 400,000,000 |  |  |  |
Interest rate on debt ( in percentage) |  |  | 2.80% |  | 2.80% | 2.80% |  |  |  |  |
Total debt |  |  | $ 399,000,000 | 0 |  |  |  |  |  |  |
Senior Notes [Member] | 3.50% Senior Notes due September 2015 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 3.50% |  | 3.50% | 3.50% |  |  |  |  |
Total debt |  |  | $ 0 | 599,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 4.60% Senior Notes due June 2044 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 4.60% |  | 4.60% | 4.60% |  |  |  |  |
Total debt |  |  | $ 549,000,000 | 549,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 2.875% Senior Notes due May 2026 (EUR 500M) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value |  |  | $ 500,000,000 |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 2.875% |  | 2.875% | 2.875% |  |  |  |  |
Total debt |  |  | $ 545,000,000 | 605,000,000 |  |  |  |  |  |  |
Senior Notes [Member] | 8.205% Junior Subordinated Notes due January 2027 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 8.205% |  | 8.205% | 8.205% |  |  |  |  |
Total debt |  |  | $ 521,000,000 | 521,000,000 |  |  |  |  |  |  |
Unsecured Debt [Member] | 4.76% Senior Notes due March 2018 (CAD 375M) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 4.76% |  | 4.76% | 4.76% |  |  |  |  |
Junior Subordinated Debt [Member] | 8.205% Junior Subordinated Notes due January 2027 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  |  | 8.205% |  | 8.205% | 8.205% |  |  |  |  |
Commercial Paper [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  | $ 50,000,000 | $ 168,000,000 |  |  |  |  |  |  |
Weighted-average interest rates (in percentage) |  |  | 0.50% | 0.35% |  |  |  |  |  |  |
Notes Payable [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  | $ 16,000,000 | $ 31,000,000 |  |  |  |  |  |  |
Notes Payable [Member] | 3.50% notes due 2024 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value |  |  |  |  |  |  |  |  |  | $ 350,000,000 | $ 250,000,000
Interest rate on debt ( in percentage) |  |  |  |  |  |  |  |  |  | 3.50% | 3.50%
Notes Payable [Member] | 4.60% Senior Notes due June 2044 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value |  |  |  |  |  |  |  |  |  |  | $ 550,000,000
Interest rate on debt ( in percentage) |  |  |  |  |  |  |  |  |  |  | 4.60%
Notes Payable [Member] | 2.875% Senior Notes due May 2026 (EUR 500M) |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt face value | € | € 500,000,000 |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) | 2.875% |  |  |  |  |  |  |  |  |  |
Senior Notes [Member] | 3.50% Senior Notes due September 2015 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) |  | 3.50% |  |  |  |  |  |  |  |  |
Extinguishment of debt |  | $ 600,000,000 |  |  |  |  |  |  |  |  |
Notes Payable [Member] | 6.25% EUR 500 debt securities due July 2014 [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate on debt ( in percentage) | 6.25% |  |  |  |  |  |  |  |  |  |
Extinguishment of debt | € | € 500,000,000 |  |  |  |  |  |  |  |  |  |
Credit Facility Expiring March 2017 [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
New credit and loan facility |  |  | 400,000,000 |  |  |  |  |  |  |  |
Commercial Paper [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term commercial paper |  |  | 50,000,000 | $ 168,000,000 |  |  |  |  |  |  |
European Credit Facility [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
New credit and loan facility | € |  |  |  |  |  |  |  |  | € 650,000,000 |  |
Credit Facility Expiring February 2020 [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
New credit and loan facility |  |  | 900,000,000 |  |  |  |  |  |  |  |
Commercial Paper [Member] | US Commercial Paper Program [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
New credit and loan facility |  |  | $ 900,000,000 |  |  |  |  |  |  |  |
Commercial Paper [Member] | European Multi-Currency Commercial Paper Program [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
New credit and loan facility | € |  |  |  |  |  | € 300,000,000 |  |  |  |  |

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