Business and Asset Actions (Project Exit Decisions) (Details) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2025 USD ($)	Jun. 30, 2026 USD ($)	Sep. 30, 2025 USD ($) plant project
Project Exit Costs
Restructuring Charges [Abstract]
Asset write-downs		$ 5,518.4
Other exit costs		1,047.4
Cumulative charges through 30 June 2026		6,565.8
Restructuring Reserve [Roll Forward]
Amount accrued at beginning of period	$ 178.3	178.3
Estimated project exit costs accrued		696.8
Changes in estimates		3.7
Cash payments		(92.1)
Amount accrued at end of period		786.7	$ 178.3
Project Exit Costs | U.S.-Based Projects
Restructuring Cost and Reserve [Line Items]
Number of projects eliminated | project			3
Project Exit Costs | Coal Gasification Plants
Restructuring Cost and Reserve [Line Items]
Number of plants to be disposed of | plant			2
FY2026 Project Exit Decisions
Restructuring Charges [Abstract]
Asset write-downs		2,210.6
Other exit costs		696.8
Cumulative charges through 30 June 2026		2,907.4
Restructuring Reserve [Roll Forward]
Amount accrued at beginning of period	0.0	0.0
Estimated project exit costs accrued		696.8
Changes in estimates		0.0
Cash payments		0.0
Amount accrued at end of period		696.8	$ 0.0
FY2025 Project Exit Decisions
Restructuring Charges [Abstract]
Asset write-downs		3,307.8
Other exit costs		350.6
Cumulative charges through 30 June 2026	28.3	3,658.4	3,630.1
Restructuring Reserve [Roll Forward]
Amount accrued at beginning of period	$ 178.3	178.3
Estimated project exit costs accrued		0.0
Changes in estimates		3.7
Cash payments		(92.1)
Amount accrued at end of period		$ 89.9	$ 178.3