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Senior Notes - Summary of Principle Terms of Senior Notes (Details) - Senior Notes $ in Millions | Dec. 31, 2016 USD ($)
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2024 Senior Notes |  |
Debt Instrument |  |
Par value (in millions) | $ 400.0 | [1]
Stated coupon | 4.25% | [1]
2025 Senior Notes |  |
Debt Instrument |  |
Par value (in millions) | $ 350.0 | [1]
Stated coupon | 3.50% | [1]
2042 Senior Notes |  |
Debt Instrument |  |
Par value (in millions) | $ 200.0 |
Stated coupon | 6.375% |
[1] | The 2024 and 2025 senior notes may be redeemed at any time, in whole or in part, at a make-whole redemption price plus accrued and unpaid interest.

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