Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 3

Fair Value Measured at Net Asset Value Per Share

Diversified Growth Assets

Diversified Growth Assets | Fair Value, Inputs, Level 1

Diversified Growth Assets | Fair Value, Inputs, Level 2

Diversified Growth Assets | Fair Value, Inputs, Level 3

Diversified Growth Assets | Fair Value Measured at Net Asset Value Per Share

Fixed Interest and Index-linked Securities

Fixed Interest and Index-linked Securities | Fair Value, Inputs, Level 1

Fixed Interest and Index-linked Securities | Fair Value, Inputs, Level 2

Fixed Interest and Index-linked Securities | Fair Value, Inputs, Level 3

Fixed Interest and Index-linked Securities | Fair Value Measured at Net Asset Value Per Share

Cash Equivalents

Cash Equivalents | Fair Value, Inputs, Level 1

Cash Equivalents | Fair Value, Inputs, Level 2

Cash Equivalents | Fair Value, Inputs, Level 3

Cash Equivalents | Fair Value Measured at Net Asset Value Per Share

Employee Benefit Plans UK Pension Assets, Fair Value Measurement by Input Level (Details) - Pension Plan - UNITED KINGDOM - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	$ 294.1	$ 252.8	$ 217.0
Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	118.1	89.8
Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	176.0	163.0
Diversified Growth Assets
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	176.0	163.0
Diversified Growth Assets \| Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Diversified Growth Assets \| Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Diversified Growth Assets \| Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Diversified Growth Assets \| Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	176.0	163.0
Fixed Interest and Index-linked Securities
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	116.8	89.6
Fixed Interest and Index-linked Securities \| Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	116.8	89.6
Fixed Interest and Index-linked Securities \| Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Fixed Interest and Index-linked Securities \| Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Fixed Interest and Index-linked Securities \| Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Cash Equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	1.3	0.2
Cash Equivalents \| Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	1.3	0.2
Cash Equivalents \| Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Cash Equivalents \| Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	0.0	0.0
Cash Equivalents \| Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Plan Assets	$ 0.0	$ 0.0