Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures, Activity in Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Pension [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	$ 759.4	$ 699.6
Fair Value, End of Year	745.7	759.4
Pension [Member] \| Level 3 [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	25.0
Fair Value, End of Year	21.6	25.0
Pension [Member] \| Private Equity [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	7.0
Fair Value, End of Year	0.0	7.0
Pension [Member] \| Private Equity [Member] \| Level 3 [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	7.0	8.0
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	(3.5)	0.1
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement	(3.5)	(1.1)
Fair Value, End of Year	0.0	7.0
Pension [Member] \| Real Estate [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	18.0
Fair Value, End of Year	21.6	18.0
Pension [Member] \| Real Estate [Member] \| Level 3 [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	18.0	18.0
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	3.6	0.0
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement	0.0	0.0
Fair Value, End of Year	21.6	18.0
Postretirement Health and Life [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	186.0	173.7
Fair Value, End of Year	201.8	186.0
Postretirement Health and Life [Member] \| Level 3 [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	1.7
Fair Value, End of Year	2.0	1.7
Postretirement Health and Life [Member] \| Private Equity [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	1.7
Fair Value, End of Year	2.0	1.7
Postretirement Health and Life [Member] \| Private Equity [Member] \| Level 3 [Member]
Activity in Level 3 [Roll Forward]
Fair Value, Beginning of Year	1.7	1.7
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held	0.8	0.0
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement	(0.5)	0.0
Fair Value, End of Year	$ 2.0	$ 1.7

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

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Balance Type:	debit
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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

+ Details

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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- Details

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