Business Segments and Related Information (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) Segment	Jun. 30, 2020 USD ($)
Business Segments [Abstract]
Number of reportable segments | Segment				4
Gross Operating Margin
Operating income		$ 1,492.6	$ 1,436.9	$ 3,187.1	$ 2,944.4
Adjustments to reconcile operating income to total segment gross operating margin (addition or subtraction indicated by sign):
Depreciation, amortization and accretion expense in operating costs and expenses	[1]	499.1	494.3	995.2	977.1
Asset impairment charges in operating costs and expenses		17.9	11.8	83.4	13.4
Net losses (gains) attributable to asset sales and related matters in operating costs and expenses		0.3	(1.6)	11.2	(1.5)
General and administrative costs		51.5	57.0	107.8	112.5
Non-refundable payments received from shippers attributable to make-up rights	[2]	22.3	13.0	41.6	29.8
Subsequent recognition of revenues attributable to make-up rights	[3]	(38.9)	(8.5)	(78.2)	(15.6)
Total segment gross operating margin		$ 2,044.8	$ 2,002.9	$ 4,348.1	$ 4,060.1

[1] Excludes amortization of major maintenance costs for reaction-based plants, which are a component of gross operating margin.

[2] Since make-up rights entail a future performance obligation by the pipeline to the shipper, these receipts are recorded as deferred revenue for GAAP purposes; however, these receipts are included in gross operating margin in the period of receipt since they are nonrefundable to the shipper.

[3] As deferred revenues attributable to make-up rights are subsequently recognized as revenue under GAAP, gross operating margin must be adjusted to remove such amounts to prevent duplication since the associated non-refundable payments were previously included in gross operating margin.