Retirement Benefits - Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Maximum average weighted maturity (in years)	10 years
UMWA Plans
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 136.1	$ 139.0	$ 178.0
% Actual Allocation	100.00%	100.00%
% Target Allocation	100.00%	100.00%
UMWA Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 0.0	$ 0.2
% Actual Allocation	0.00%	0.00%
% Target Allocation	0.00%	0.00%
UMWA Plans | U.S. large-cap(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	22.00%	18.00%
% Target Allocation	24.00%	22.00%
UMWA Plans | U.S. large-cap(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 29.3	$ 25.6
UMWA Plans | U.S. small/mid-cap(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	10.00%	7.00%
% Target Allocation	11.00%	10.00%
UMWA Plans | U.S. small/mid-cap(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 13.2	$ 10.0
UMWA Plans | International(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	24.00%	20.00%
% Target Allocation	26.00%	24.00%
UMWA Plans | International(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 32.1	$ 28.2
UMWA Plans | Emerging markets(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	3.00%	4.00%
% Target Allocation	4.00%	4.00%
UMWA Plans | Emerging markets(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 5.1	$ 4.9
UMWA Plans | Dynamic asset allocation(c)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	7.00%	6.00%
% Target Allocation	7.00%	7.00%
UMWA Plans | Dynamic asset allocation(c) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 8.9	$ 8.5
UMWA Plans | High yield(e)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	2.00%	2.00%
% Target Allocation	2.00%	2.00%
UMWA Plans | High yield(e) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 2.6	$ 2.4
UMWA Plans | Emerging markets(f)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	4.00%	4.00%
% Target Allocation	4.00%	4.00%
UMWA Plans | Emerging markets(f) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 5.1	$ 5.0
UMWA Plans | Multi asset real return(i)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	4.00%	4.00%
% Target Allocation	5.00%	5.00%
UMWA Plans | Multi asset real return(i) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 6.1	$ 6.1
UMWA Plans | Core property(g) (l)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	10.00%	15.00%
% Target Allocation	5.00%	10.00%
UMWA Plans | Core property(g) (l) | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 14.7	$ 20.6
UMWA Plans | Structured credit
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	6.00%	9.00%
% Target Allocation	5.00%	5.00%
UMWA Plans | Structured credit | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 8.3	$ 12.8
UMWA Plans | Global private equity(j) (l)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 9.6	$ 11.9
% Actual Allocation	7.00%	9.00%
% Target Allocation	7.00%	7.00%
UMWA Plans | Energy debt
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 1.1	$ 2.8
% Actual Allocation	1.00%	2.00%
% Target Allocation	0.00%	0.00%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Maximum average weighted maturity (in years)	5 years
Minimum | Long duration - mutual fund(d)
Defined Benefit Plan Disclosure [Line Items]
Portfolio duration (in years)	10 years
Maximum
Defined Benefit Plan Disclosure [Line Items]
Maximum average weighted maturity (in years)	7 years
Maximum | Long duration - mutual fund(d)
Defined Benefit Plan Disclosure [Line Items]
Portfolio duration (in years)	15 years
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 611.6	$ 596.3	764.8
% Actual Allocation	100.00%	100.00%
% Target Allocation	100.00%	100.00%
U.S. Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 3.8	$ 3.8
% Actual Allocation	0.00%	0.00%
% Target Allocation	0.00%	0.00%
U.S. Plans | U.S. large-cap(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	9.00%	15.00%
% Target Allocation	13.00%	16.00%
U.S. Plans | U.S. large-cap(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 57.6	$ 90.2
U.S. Plans | U.S. small/mid-cap(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	3.00%	5.00%
% Target Allocation	4.00%	5.00%
U.S. Plans | U.S. small/mid-cap(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 15.4	$ 27.9
U.S. Plans | International(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	10.00%	17.00%
% Target Allocation	14.00%	17.00%
U.S. Plans | International(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 63.7	$ 99.2
U.S. Plans | Emerging markets(a)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	1.00%	2.00%
% Target Allocation	1.00%	2.00%
U.S. Plans | Emerging markets(a) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 4.5	$ 11.5
U.S. Plans | Dynamic asset allocation(c)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	3.00%	5.00%
% Target Allocation	3.00%	5.00%
U.S. Plans | Dynamic asset allocation(c) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 15.6	$ 28.1
U.S. Plans | Long duration - mutual fund(d)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	62.00%	44.00%
% Target Allocation	60.00%	45.00%
U.S. Plans | Long duration - mutual fund(d) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 317.4	$ 189.4
U.S. Plans | Long duration - Treasury strips(d) | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 58.9	$ 74.9
U.S. Plans | Core property(g) (l)
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	5.00%	6.00%
% Target Allocation	2.00%	5.00%
U.S. Plans | Core property(g) (l) | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 33.0	$ 36.2
U.S. Plans | Structured credit
Defined Benefit Plan Disclosure [Line Items]
% Actual Allocation	7.00%	6.00%
% Target Allocation	3.00%	5.00%
U.S. Plans | Structured credit | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 41.7	$ 35.1
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 259.3	$ 245.5	$ 360.3
% Actual Allocation	100.00%	100.00%
% Target Allocation	100.00%	100.00%
Non-U.S. Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 0.9	$ 0.7
% Actual Allocation	0.00%	0.00%
% Target Allocation	0.00%	0.00%
Non-U.S. Plans | Equity securities:
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 20.0	$ 30.0
% Actual Allocation	8.00%	12.00%
% Target Allocation	10.00%	13.00%
Non-U.S. Plans | U.S. equity funds(a)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 7.4	$ 9.6
Non-U.S. Plans | Canadian equity funds(a)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	1.6	3.6
Non-U.S. Plans | European equity funds(a)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	1.4	1.4
Non-U.S. Plans | Other global equity funds(a)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	9.6	15.4
Non-U.S. Plans | Fixed-income securities:
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 130.0	$ 113.9
% Actual Allocation	50.00%	47.00%
% Target Allocation	49.00%	47.00%
Non-U.S. Plans | Long duration - mutual fund(d)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 61.4	$ 59.5
Non-U.S. Plans | High yield(e)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	0.7	0.7
Non-U.S. Plans | Emerging markets(f)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	0.8	0.7
Non-U.S. Plans | Canadian fixed-income securities(b)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	55.4	42.0
Non-U.S. Plans | European fixed-income funds(c)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	11.7	11.0
Non-U.S. Plans | Other types of investments:
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 108.4	$ 100.9
% Actual Allocation	10.00%	10.00%
% Target Allocation	7.00%	7.00%
Non-U.S. Plans | Guaranteed contract value
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 82.6	$ 75.8
% Actual Allocation	32.00%	31.00%
% Target Allocation	34.00%	33.00%
Non-U.S. Plans | Property funds(h)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 11.1	$ 9.6
Non-U.S. Plans | Global infrastructure fund(i)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	7.5	6.8
Non-U.S. Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value	$ 7.2	$ 8.7