Joint Ownership Agreements - Equity Method Investments - Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 1,549	$ 6
Successor [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,541
Successor [Member] | SNG [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	1,394
Current assets	95
Property, plant, and equipment	2,451
Deferred charges and other assets	129
Total Assets	2,675
Current liabilities	588
Long-term debt	706
Other deferred charges and other liabilities	22
Total Liabilities	1,316
Total Stockholders' Equity	1,359
Total Liabilities and Stockholders' Equity	2,675
Successor [Member] | Triton [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	44
Successor [Member] | Horizon Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	30
Successor [Member] | PennEast Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	22
Successor [Member] | Atlantic Coast Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	33
Successor [Member] | Pivotal JAX LNG, LLC [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	16
Successor [Member] | Other [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries	$ 2
Predecessor [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		80
Predecessor [Member] | SNG [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		0
Predecessor [Member] | Triton [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		49
Predecessor [Member] | Horizon Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		14
Predecessor [Member] | PennEast Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		9
Predecessor [Member] | Atlantic Coast Pipeline [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		7
Predecessor [Member] | Pivotal JAX LNG, LLC [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		0
Predecessor [Member] | Other [Member] | Southern Company Gas [Member]
Schedule of Equity Method Investments [Line Items]
Equity investments in unconsolidated subsidiaries		$ 1