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Retirement Benefits (Details 7) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Amortization of net actuarial loss | $ 87.2 | $ 76.5 | $ 71.6
Amortization to net income (loss) of net prior service cost (credits) | (2.6) | (2.6) | (1.6)
Net loss arising during the period | (180.5) | (141.4) | (42.7)
Pension Benefits [Member] |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Beginning of year accumulated other comprehensive loss | (1,470.3) | (1,426.1) |
Amortization of net actuarial loss | 73.7 | 65.9 |
Amortization to net income (loss) of net prior service cost (credits) | 0.3 | 0.3 |
Net loss arising during the period | (173.4) | (110.4) |
End of year accumulated other comprehensive loss | (1,569.7) | (1,470.3) | (1,426.1)
Net change in accumulated other comprehensive loss | (99.4) | (44.2) |
Other Postretirement Benefits |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Beginning of year accumulated other comprehensive loss | (107.0) | (83.7) |
Amortization of net actuarial loss | 13.5 | 10.6 |
Amortization to net income (loss) of net prior service cost (credits) | (2.9) | (2.9) |
Net loss arising during the period | (7.1) | (31.0) |
End of year accumulated other comprehensive loss | (103.5) | (107.0) | $ (83.7)
Net change in accumulated other comprehensive loss | $ 3.5 | $ (23.3) |

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