Employee Benefits - Summary of Assets for Reported NAV Used to Estimate Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair Value	$ 900.0	$ 874.9	$ 998.3
Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair Value	900.0	874.9
Fair Value, Measurements, Recurring | Net Asset Value per Share
Defined Benefit Plan Disclosure [Line Items]
Fair Value	536.2	536.8
Fair Value, Measurements, Recurring | Private Equities
Defined Benefit Plan Disclosure [Line Items]
Unfunded Commitments	1.7	2.8
Fair Value, Measurements, Recurring | Private Equities | Net Asset Value per Share
Defined Benefit Plan Disclosure [Line Items]
Fair Value	127.0	155.2
Fair Value, Measurements, Recurring | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Unfunded Commitments	4.1	0.5
Fair Value, Measurements, Recurring | Fixed Income | Net Asset Value per Share
Defined Benefit Plan Disclosure [Line Items]
Fair Value	231.4	189.2
Fair Value, Measurements, Recurring | Equities | Net Asset Value per Share
Defined Benefit Plan Disclosure [Line Items]
Fair Value	$ 81.9	$ 84.0
Fair Value, Measurements, Recurring | Equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Redemption Notice Period	0 days	3 days
Fair Value, Measurements, Recurring | Equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Redemption Notice Period	30 days	30 days
Fair Value, Measurements, Recurring | Absolute Return | Net Asset Value per Share
Defined Benefit Plan Disclosure [Line Items]
Fair Value	$ 95.9	$ 108.4
Fair Value, Measurements, Recurring | Absolute Return | Minimum
Defined Benefit Plan Disclosure [Line Items]
Redemption Notice Period	3 days	2 days
Fair Value, Measurements, Recurring | Absolute Return | Maximum
Defined Benefit Plan Disclosure [Line Items]
Redemption Notice Period	75 days	45 days