Variable Interest Entities (Pipeline Investments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Investments in joint ventures	$ 2,067	$ 1,936
VIE not primary beneficiary
Variable Interest Entities [Line Items]
Investments in joint ventures	$ 1,614	1,479
ACP
Variable Interest Entities [Line Items]
Ownership percentage	47.00%
ACP \| VIE not primary beneficiary
Variable Interest Entities [Line Items]
Investments in joint ventures	$ 1,243	1,179
Constitution
Variable Interest Entities [Line Items]
Ownership percentage	24.00%
Pipeline Investments \| VIE not primary beneficiary
Variable Interest Entities [Line Items]
Investments in joint ventures	$ 1,243	$ 1,179

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant