Pension Plans and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer contributions	$ 520.0	$ 550.0	$ 334.0
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	25.0	25.0	12.0
Multiemployer plans, plan contributions	19.0	18.0	18.0
Benefit obligation	6,462.0	6,239.0	5,841.0
Net periodic benefit cost	$ (218.0)	(131.0)	(6.0)
Pension Plan \| Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	20.00%
Pension Plan \| Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	68.00%
Pension Plan \| Real Estate Investment
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	6.00%
Pension Plan \| Private equity investments
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	3.00%
Pension Plan \| Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Target investment allocations	3.00%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Multiemployer plans, plan contributions	$ 54.0	57.0	58.0
Benefit obligation	226.0	246.0
Net periodic benefit cost	$ 12.0	$ 7.0	$ 2.0

Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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