Fair Value Measurements - Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair value of financial instruments
Preferred stock of subsidiary	$ 30.4	$ 30.4
Long-term debt, including current portion	12,450.5	11,858.3
Finance lease obligation	63.4	45.9
Carrying amount
Fair value of financial instruments
Preferred stock of subsidiary	30.4	30.4
Long-term debt, including current portion	12,450.5	11,858.3
Finance lease obligation	63.4	45.9
Fair value
Fair value of financial instruments
Preferred stock of subsidiary	32.3	29.5
Long-term debt, including current portion	$ 14,343.2	$ 13,035.9

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.

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