Fair Value Measurements - Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financial instruments
Preferred stock of subsidiary	$ 30.4	$ 30.4
Long-term debt, including current portion	16,631.1	15,464.2
Finance lease obligation	145.9	183.2
Carrying amount
Financial instruments
Preferred stock of subsidiary	30.4	30.4
Long-term debt, including current portion	16,631.1	15,464.2
Finance lease obligation	145.9	183.2
Fair value
Financial instruments
Preferred stock of subsidiary	21.4	22.7
Long-term debt, including current portion	$ 15,564.3	$ 13,921.3

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
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-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant