SOUTHERN Co GAS (GAS) 10-Q 4 Nov 16 2016 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	9 Months Ended
	Sep. 30, 2016shares
Document and Entity Information [Abstract]
Entity Registrant Name	SOUTHERN Co GAS
Trading Symbol
Document Type	10-Q
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding	100
Amendment Flag	false
Entity Central Index Key	1,004,155
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Natural gas revenues (includes revenue taxes of $9, $9, $9, $57, and $83 for the periods presented, respectively)	$ 518
Other revenues	25
Total operating revenues	543
Operating Expenses:
Cost of natural gas	133
Cost of other sales	2
Other operations and maintenance	216
Depreciation and amortization	116
Taxes other than income taxes	29
Merger-related expenses	35
Total operating expenses	531
Operating Income	12
Other Income and (Expense):
Allowance for equity funds used during construction	0
Interest expense, net of amounts capitalized	(39)
Earnings from equity method investments	29
Other income (expense), net	9
Total other income and (expense)	(1)
Earnings Before Income Taxes	11
Income taxes	7
Consolidated Net Income	4
Less: Net income attributable to noncontrolling interest	0
Consolidated Net Income Attributable to Southern Company Gas	$ 4
Predecessor [Member]
Natural gas revenues (includes revenue taxes of $9, $9, $9, $57, and $83 for the periods presented, respectively)		$ 553	$ 1,841	$ 2,887
Other revenues		31	64	92
Total operating revenues		584	1,905	2,979
Operating Expenses:
Cost of natural gas		140	755	1,282
Cost of other sales		6	14	21
Other operations and maintenance		218	454	676
Depreciation and amortization		98	206	293
Taxes other than income taxes		28	99	142
Merger-related expenses		35	56	35
Total operating expenses		525	1,584	2,449
Operating Income		59	321	530
Other Income and (Expense):
Allowance for equity funds used during construction		1	2	3
Interest expense, net of amounts capitalized		(43)	(96)	(129)
Earnings from equity method investments		2	2	4
Other income (expense), net		0	3	3
Total other income and (expense)		(40)	(89)	(119)
Earnings Before Income Taxes		19	232	411
Income taxes		7	87	150
Consolidated Net Income		12	145	261
Less: Net income attributable to noncontrolling interest		1	14	15
Consolidated Net Income Attributable to Southern Company Gas		$ 11	$ 131	$ 246

Condensed Consolidated Stateme3

Condensed Consolidated Statements of Income (Unaudited) (Parentheticals) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Operating revenues, revenue taxes	$ 9
Predecessor [Member]
Operating revenues, revenue taxes		$ 9	$ 57	$ 83

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Consolidated Net Income	$ 4
Qualifying hedges:
Changes in fair value, net of tax of $(2), $(18), $(2), $(23) and $(1), respectively	(3)
Reclassification adjustment for amounts included in net income, net of tax of less than $1 for each period presented	0
Pension and other post retirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax of $0, $2, $0, $4 and $6, respectively	0
Total other comprehensive income (loss)	(3)
Less: Comprehensive income attributable to noncontrolling interest	0
Consolidated Comprehensive Income (Loss) Attributable to Southern Company Gas	$ 1
Predecessor [Member]
Consolidated Net Income		$ 12	$ 145	$ 261
Qualifying hedges:
Changes in fair value, net of tax of $(2), $(18), $(2), $(23) and $(1), respectively		(30)	(41)	(3)
Reclassification adjustment for amounts included in net income, net of tax of less than $1 for each period presented		1	1	5
Pension and other post retirement benefit plans:
Reclassification adjustment for amounts included in net income, net of tax of $0, $2, $0, $4 and $6, respectively		2	5	9
Total other comprehensive income (loss)		(27)	(35)	11
Less: Comprehensive income attributable to noncontrolling interest		0	14	15
Consolidated Comprehensive Income (Loss) Attributable to Southern Company Gas		$ (15)	$ 96	$ 257

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parentheticals) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Changes in fair value, tax	$ 2
Reclassification adjustment for amounts of qualifying hedges included in net income, tax	0
Reclassification adjustment for amounts of pension and other post retirement benefit plans included in net income, tax	$ 0
Predecessor [Member]
Changes in fair value, tax		$ 18	$ 23	$ 1
Reclassification adjustment for amounts of qualifying hedges included in net income, tax		0	0	0
Reclassification adjustment for amounts of pension and other post retirement benefit plans included in net income, tax		$ 2	$ 4	$ 6

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Operating Activities:
Consolidated Net Income	$ 4
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total	116
Deferred income taxes	(30)
Stock based compensation expense	11
Hedge settlements	(35)
Pension, postretirement, and other employee benefits	(123)
Goodwill impairment	0
Other, net	(30)
Changes in certain current assets and liabilities —
-Receivables	(18)
-Natural gas for sale	(222)
-Other current assets	(35)
-Accounts payable	78
-Accrued taxes	(11)
-Accrued compensation	(36)
-Other current liabilities	(11)
Net cash provided from (used for) operating activities	(342)
Investing Activities:
Property additions	(287)
Cost of removal, net of salvage	(21)
Change in construction payables, net	9
Investment in unconsolidated subsidiaries	(1,421)
Returned investment in unconsolidated subsidiaries	2
Other investing activities	3
Net cash used for investing activities	(1,715)
Financing Activities:
Increase (decrease) in notes payable, net	472
Proceeds —
First mortgage bonds	0
Senior notes	900
Capital contributions from parent company	1,089
Redemptions and repurchases —
First mortgage bonds	0
Senior notes	(300)
Distribution to noncontrolling interest	0
Payment of common stock dividends	(63)
Other financing activities	(8)
Net cash provided from (used for) financing activities	2,090
Net Change in Cash and Cash Equivalents	33
Cash and Cash Equivalents at Beginning of Period	15
Cash and Cash Equivalents at End of Period	48	$ 15
Cash paid (received) during the period for —
Interest (net of $2, $3, and $3 capitalized, respectively)	86
Income taxes, net	54
Noncash transactions — Accrued property additions at end of period	50
Predecessor [Member]
Operating Activities:
Consolidated Net Income		145	$ 261
Adjustments to reconcile consolidated net income to net cash provided from operating activities —
Depreciation and amortization, total		206	293
Deferred income taxes		8	38
Stock based compensation expense		20	22
Hedge settlements		(26)	0
Pension, postretirement, and other employee benefits		5	18
Goodwill impairment		0	14
Other, net		80	117
Changes in certain current assets and liabilities —
-Receivables		181	761
-Natural gas for sale		273	62
-Other current assets		188	168
-Accounts payable		43	(313)
-Accrued taxes		41	(19)
-Accrued compensation		(21)	(20)
-Other current liabilities		(30)	8
Net cash provided from (used for) operating activities		1,113	1,410
Investing Activities:
Property additions		(509)	(677)
Cost of removal, net of salvage		(32)	(68)
Change in construction payables, net		(7)	0
Investment in unconsolidated subsidiaries		(14)	(8)
Returned investment in unconsolidated subsidiaries		3	11
Other investing activities		0	1
Net cash used for investing activities		(559)	(741)
Financing Activities:
Increase (decrease) in notes payable, net		(896)	(289)
Proceeds —
First mortgage bonds		250	0
Senior notes		350	0
Capital contributions from parent company		0	0
Redemptions and repurchases —
First mortgage bonds		(125)	0
Senior notes		0	(200)
Distribution to noncontrolling interest		(19)	(18)
Payment of common stock dividends		(128)	(183)
Other financing activities		10	9
Net cash provided from (used for) financing activities		(558)	(681)
Net Change in Cash and Cash Equivalents		(4)	(12)
Cash and Cash Equivalents at Beginning of Period	$ 15	19	31
Cash and Cash Equivalents at End of Period		15	19
Cash paid (received) during the period for —
Interest (net of $2, $3, and $3 capitalized, respectively)		119	145
Income taxes, net		(100)	(26)
Noncash transactions — Accrued property additions at end of period		$ 41	$ 31

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows (Unaudited) Condensed Consolidated Statements of Cash Flows (Unaudited) (Parentheticals) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Interest capitalized	$ 2
Predecessor [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Interest capitalized		$ 3	$ 3

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Successor [Member]
Current Assets:
Cash and cash equivalents	$ 48
Receivables —
Energy marketing receivable	526
Customer accounts receivable	190
Unbilled revenues	63
Other accounts and notes receivable	55
Accumulated provision for uncollectible accounts	(29)
Materials and supplies	27
Natural gas for sale	627
Assets from risk management activities, net of collateral	98
Prepaid expenses	76
Other regulatory assets, current	69
Other	9
Total current assets	1,759
Property, Plant, and Equipment:
In service	14,267
Less accumulated depreciation	4,384
Plant in service, net of depreciation	9,883
Construction work in progress	434
Total property, plant, and equipment	10,317
Other Property and Investments:
Goodwill	5,937
Other intangible assets, net of amortization of $20 and $68 at September 30, 2016 and December 31, 2015, respectively	380
Equity investments in unconsolidated subsidiaries	1,531
Miscellaneous property and investments	22
Total other property and investments	7,870
Deferred Charges and Other Assets:
Other regulatory assets, deferred	1,105
Other deferred charges and assets	134
Total deferred charges and other assets	1,239
Total assets	21,185
Current liabilities
Securities due within one year	142
Notes payable	586
Energy marketing trade payables	533
Accounts payable	276
Customer deposits	172
Accrued taxes —
Accrued income taxes	29
Other accrued taxes	60
Accrued interest	46
Accrued compensation	35
Liabilities from risk management activities, net of collateral	47
Other regulatory liabilities, current	62
Accrued environmental remediation liabilities, current	59
Mandatorily redeemable noncontrolling interest	174
Other current liabilities	100
Total current liabilities	2,321
Long-term Debt	5,272
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes	1,900
Accumulated deferred investment tax credits	19
Employee benefit obligations	564
Other cost of removal obligations	1,609
Other regulatory liabilities, deferred	51
Accrued environmental remediation liabilities, deferred	374
Other deferred credits and liabilities	40
Total deferred credits and other liabilities	4,557
Total Liabilities	12,150
Common Stockholders' Equity:
Par Value	0
Paid-in capital	9,097
Treasury, at cost	0
Retained earnings (accumulated deficit)	(59)
Accumulated other comprehensive loss	(3)
Total Common Stockholders’ Equity	9,035
Noncontrolling Interest	0
Total Stockholders' Equity	9,035
Total Liabilities and Stockholders' Equity	$ 21,185
Predecessor [Member]
Current Assets:
Cash and cash equivalents		$ 19
Receivables —
Energy marketing receivable		445
Customer accounts receivable		316
Unbilled revenues		140
Other accounts and notes receivable		68
Accumulated provision for uncollectible accounts		(29)
Materials and supplies		29
Natural gas for sale		622
Assets from risk management activities, net of collateral		206
Prepaid expenses		218
Other regulatory assets, current		68
Other		13
Total current assets		2,115
Property, Plant, and Equipment:
In service		12,152
Less accumulated depreciation		2,775
Plant in service, net of depreciation		9,377
Construction work in progress		414
Total property, plant, and equipment		9,791
Other Property and Investments:
Goodwill		1,813
Other intangible assets, net of amortization of $20 and $68 at September 30, 2016 and December 31, 2015, respectively		109
Equity investments in unconsolidated subsidiaries		80
Miscellaneous property and investments		23
Total other property and investments		2,025
Deferred Charges and Other Assets:
Other regulatory assets, deferred		670
Other deferred charges and assets		153
Total deferred charges and other assets		823
Total assets		14,754
Current liabilities
Securities due within one year		545
Notes payable		1,010
Energy marketing trade payables		418
Accounts payable		255
Customer deposits		165
Accrued taxes —
Accrued income taxes		13
Other accrued taxes		46
Accrued interest		49
Accrued compensation		92
Liabilities from risk management activities, net of collateral		44
Other regulatory liabilities, current		81
Accrued environmental remediation liabilities, current		67
Mandatorily redeemable noncontrolling interest		0
Other current liabilities		133
Total current liabilities		2,918
Long-term Debt		3,275
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes		1,943
Accumulated deferred investment tax credits		20
Employee benefit obligations		515
Other cost of removal obligations		1,591
Other regulatory liabilities, deferred		53
Accrued environmental remediation liabilities, deferred		364
Other deferred credits and liabilities		100
Total deferred credits and other liabilities		4,586
Total Liabilities		10,779
Common Stockholders' Equity:
Par Value		603
Paid-in capital		2,099
Treasury, at cost		(8)
Retained earnings (accumulated deficit)		1,421
Accumulated other comprehensive loss		(186)
Total Common Stockholders’ Equity		3,929
Noncontrolling Interest		46
Total Stockholders' Equity		3,975
Total Liabilities and Stockholders' Equity		$ 14,754

Condensed Consolidated Balance9

Condensed Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Successor [Member]
Accumulated Amortization	$ 20
Common stock, par value (in dollars per share)	$ 0.01
Common stock, shares authorized	100,000,000
Common stock, shares outstanding	100
Treasury shares, shares	0
Predecessor [Member]
Accumulated Amortization		$ 68
Common stock, par value (in dollars per share)		$ 5
Common stock, shares authorized		750,000,000
Common stock, shares outstanding		120,400,000
Treasury shares, shares		200,000

Introduction

Introduction	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Introduction	INTRODUCTION Southern Company Gas (formerly known as AGL Resources Inc.) is an energy services holding company whose primary business is the distribution of natural gas through natural gas distribution utilities. On July 1, 2016, Southern Company and Southern Company Gas completed the Merger and Southern Company Gas became a wholly-owned, direct subsidiary of Southern Company and, on July 11, 2016, changed its name to Southern Company Gas. See Note (I) for additional information regarding the Merger. The condensed consolidated quarterly financial statements included herein have been prepared, without audit, pursuant to the rules and regulations of the SEC. The condensed consolidated balance sheet as of December 31, 2015 has been derived from the audited consolidated financial statements of Southern Company Gas. In the opinion of management, the information furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended September 30, 2016 and 2015 . Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although Southern Company Gas believes that the disclosures are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Consolidated Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for natural gas, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year. Pursuant to the Merger, Southern Company has pushed down the application of the acquisition method of accounting to the consolidated financial statements of Southern Company Gas such that the assets and liabilities of Southern Company Gas are recorded at their respective fair values, and goodwill has been established for the excess of the purchase price over the fair value of net identifiable assets. Accordingly, the consolidated financial statements of Southern Company Gas for periods before and after July 1, 2016 (acquisition date) reflect different bases of accounting, and the financial positions and results of operations of those periods are not comparable. Throughout the consolidated financial statements and notes to those financial statements, periods prior to July 1, 2016 are identified as "predecessor," while periods after the acquisition date are identified as "successor." Certain prior year data and current year predecessor period data presented in the financial statements have been modified or reclassified to conform to the presentation used by Southern Company Gas’ new parent company, Southern Company. Changes to the consolidated statements of income include classifying operating revenues as natural gas revenues and other revenues as well as classifying cost of goods sold as cost of natural gas and cost of other sales, and presenting interest expense and allowance for equity funds used during construction on a gross basis. Changes to the consolidated statements of cash flows include revised financial statement line item descriptions to align with the new balance sheet descriptions and expanded line items within each type of cash flow activity. Changes to the consolidated balance sheets include changing certain captions to conform to the presentation of Southern Company. Such reclassification did not have a significant impact on the results of operations, financial position, or cash flows of Southern Company Gas. Recently Issued Accounting Standards On November 20, 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes (ASU 2015-17), which simplifies the presentation of deferred income taxes. ASU 2015-17 requires deferred tax assets and liabilities to be presented as non-current in a classified balance sheet and is effective for fiscal years beginning after December 15, 2016, including interim periods within that reporting period. As permitted, Southern Company Gas elected to early adopt the guidance as of September 30, 2016 and applied its provisions retrospectively to each prior period presented for comparative purposes. Prior to the adoption of ASU 2015-17, all deferred income tax assets and liabilities were required to be separated into current and non-current amounts. The new guidance resulted in a reclassification of $31 million deferred income taxes, current to non-current accumulated deferred income taxes in Southern Company Gas' December 31, 2015 balance sheet. Other than the reclassification, the adoption of ASU 2015-17 did not have an impact on the results of operations, financial position, or cash flows of Southern Company Gas. On February 25, 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changes the recognition, measurement, and presentation of expense associated with leases and provides clarification regarding the identification of certain components of contracts that would represent a lease. The accounting required by lessors is relatively unchanged. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. Southern Company Gas is currently evaluating the new standard and has not yet determined its ultimate impact; however, adoption of ASU 2016-02 is expected to have a significant impact on Southern Company Gas' balance sheet. On March 30, 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (ASU 2016-09). ASU 2016-09 changes the accounting for income taxes and the cash flow presentation for share-based payment award transactions. Most significantly, entities are required to recognize all excess tax benefits and deficiencies related to the exercise or vesting of stock compensation as income tax expense or benefit in the income statement. Southern Company Gas currently recognizes any excess tax benefits and deficiencies related to the exercise and vesting of stock compensation in additional paid-in capital. ASU 2016-09 is effective for fiscal years beginning after December 15, 2016. Early adoption is permitted and Southern Company Gas intends to adopt the ASU in the fourth quarter 2016. The adoption is not expected to have a material impact on the results of operations, financial position, or cash flows of Southern Company Gas. Goodwill and Other Intangible Assets Goodwill and other intangible assets consisted of the following: Successor – At September 30, 2016 Estimated Useful Life Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net (in millions) Other intangible assets subject to amortization: Gas marketing services Customer relationships 11-14 years $ 221 $ (15 ) $ 206 Trade names 10-28 years 115 (1 ) 114 Wholesale gas services Storage and transportation contracts 1-5 years 64 (4 ) 60 Total other intangible assets subject to amortization $ 400 $ (20 ) $ 380 Goodwill: Gas distribution operations $ 4,672 $ — $ 4,672 Gas marketing services 1,265 — 1,265 Total goodwill $ 5,937 $ — $ 5,937 Amortization expense associated with other intangible assets during the successor period July 1, 2016 through September 30, 2016 and the predecessor period January 1, 2016 through June 30, 2016 was $20 million and $8 million , respectively. Amortization expense for wholesale gas services is recorded as a reduction to operating revenues. At December 31, 2015, other intangible assets consisted of customer relationships and trade names within the gas marketing services segment with a net carrying amount of $109 million . The increases in goodwill and other intangible assets relate to purchase accounting adjustments associated with the Merger. See Note (I) for additional information. Amortization expense for the years 2017-2021 associated with other intangible assets is expected to be as follows: Amortization Expense (in millions) 2017 $ 73 2018 58 2019 40 2020 28 2021 21

Contingencies and Regulatory Ma

Contingencies and Regulatory Matters	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Regulatory Matters	CONTINGENCIES AND REGULATORY MATTERS See Note 12 to the consolidated financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional information relating to various lawsuits, other contingencies, and regulatory matters. Also, see Notes 3 and 4 to the consolidated financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional information relating to regulatory matters. General Litigation Matters Southern Company Gas is subject to certain claims and legal actions arising in the ordinary course of business. The ultimate outcome of such pending or potential litigation against Southern Company Gas cannot be predicted at this time; however, for current proceedings not specifically reported herein or in Note 12 to the consolidated financial statements of Southern Company Gas in Item 8 of the Form 10-K, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on Southern Company Gas' financial statements. Nicor Gas and Nicor Energy Services Company, wholly-owned subsidiaries of Southern Company Gas, and Nicor Inc. are defendants in a putative class action initially filed in September 2011 in state court in Cook County, Illinois. The plaintiffs purport to represent a class of the customers who purchased the Gas Line Comfort Guard product from Nicor Energy Services Company and variously allege that the marketing, sale, and billing of the Gas Line Comfort Guard product violated the Illinois Consumer Fraud and Deceptive Business Practices Act, constituting common law fraud and resulting in unjust enrichment of these entities. The plaintiffs seek, on behalf of the classes they purport to represent, actual and punitive damages, interest, costs, attorney fees, and injunctive relief. On October 26, 2016, the court held a hearing on the plaintiffs' motion for class certification and the defendants' motion for summary judgment on all of the plaintiffs' claims. The ultimate outcome of this matter cannot be determined at this time. Environmental Remediation Southern Company Gas must comply with environmental laws and regulations that cover the handling and disposal of waste and releases of hazardous substances. Under these various laws and regulations, Southern Company Gas could incur substantial costs to clean up affected sites. The natural gas distribution utilities in Illinois, New Jersey, Georgia, and Florida have each received authority from their respective state regulators to recover approved environmental compliance costs through regulatory mechanisms. Southern Company Gas is subject to environmental remediation liabilities associated with former manufactured gas plant sites in five different states. Accrued environmental remediation costs of $433 million have been recorded in the consolidated balance sheets, $59 million of which is expected to be incurred over the next 12 months. These environmental remediation expenditures are recoverable from customers through rate mechanisms approved by the applicable state regulatory agencies, with the exception of one site representing $5 million of the total accrued remediation costs. The ultimate outcome of these matters cannot be determined at this time; however, these matters are not expected to have a material impact on Southern Company Gas' financial statements. In September 2015, the EPA filed an administrative complaint and notice of opportunity for hearing against Nicor Gas. The complaint alleges violation of the regulatory requirements applicable to polychlorinated biphenyls in the Nicor Gas distribution system and the EPA seeks a total civil penalty of approximately $0.3 million . The ultimate outcome of this matter cannot be predicted at this time; however, the final disposition of this matter is not expected to have a material impact on the results of operations, financial position, or cash flows of Southern Company Gas. Regulatory Matters See Note 4 to the consolidated financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional information regarding Southern Company Gas' recovery of costs through various regulatory clauses and accounting orders. Regulatory Infrastructure Programs Atlanta Gas Light On August 1, 2016, Atlanta Gas Light filed a petition with the Georgia PSC for approval of a four -year extension of its Integrated System Reinforcement Program. If approved as filed, Atlanta Gas Light will be allowed to invest an additional $177 million to improve and upgrade its core gas distribution system in years 2017 through 2020. The ultimate outcome of this matter cannot be determined at this time. Virginia Natural Gas On March 9, 2016 , the Virginia Commission approved the Steps to Advance Virginia's Energy II program to replace more than 200 miles of aging pipeline infrastructure. Under this program, Virginia Natural Gas is allowed to invest up to $30 million in 2016 and $35 million annually in years 2017 through 2021 on qualifying infrastructure projects. Base Rate Case On September 1, 2016, Elizabethtown Gas filed a general base rate case with the New Jersey BPU as required under its Aging Infrastructure Replacement program, requesting an additional revenue requirement of $19 million , which reflects an allowed return on equity of 10.25% . Southern Company Gas expects the New Jersey BPU to issue an order on the filing in the third quarter 2017. The ultimate outcome of this matter cannot be determined at this time. Customer Refunds In the third quarter 2016, Elizabethtown Gas provided rate credits of $18 million to its customers in accordance with the Merger approval from the New Jersey BPU. These rate credits were distributed as direct per-customer credits and were allocated among Elizabethtown Gas' customer classes based on the base rate revenues reflected in the rates that resulted from its most recent base rate proceeding. Unrecognized Ratemaking Amounts The following table illustrates Southern Company Gas' authorized ratemaking amounts that are not recognized on its balance sheets. These amounts are primarily composed of an allowed equity rate of return on assets associated with certain of Southern Company Gas' regulatory infrastructure programs. These amounts will be recognized as revenues in Southern Company Gas' financial statements in the periods they are billable to customers. Successor Predecessor September 30, 2016 December 31, 2015 (in millions) (in millions) Atlanta Gas Light (*) $ 109 $ 103 Virginia Natural Gas 12 12 Elizabethtown Gas 6 4 Nicor Gas 3 3 Total $ 130 $ 122 (*) In October 2015, Atlanta Gas Light received an order from the Georgia PSC, which included a final determination of the true-up recovery related to the PRP that allows Atlanta Gas Light to recover $144 million of the $178 million of incurred and allowed costs that were deferred for future recovery. Gas Cost Prudence Review In 2014, the Illinois Commission Staff and the CUB filed testimony in the Nicor Gas 2003 gas cost prudence review disputing certain gas loan transactions offered by Nicor Gas under its Chicago Hub services and requesting refunds of $18 million and $22 million , respectively. Nicor Gas filed surrebuttal testimony later in 2014 disputing that any refund was due, as Nicor Gas was authorized to enter into these transactions and revenues associated with such transactions reduced ratepayers’ costs as either credits to the purchase gas adjustment or reductions to base rates consistent with then-current Illinois Commission orders governing these activities. In July 2015, the administrative law judge issued a proposed order concluding that Nicor Gas’ supply costs and purchases in 2003 were prudent, its reconciliation of the related costs was proper, and the propositions by the Illinois Commission Staff and the CUB were based on hindsight speculation, which is expressly prohibited in a prudence review examination. In November 2015, the Illinois Commission granted the CUB's petition for a rehearing on this matter. On February 10, 2016, the administrative law judge issued a proposed order on the rehearing affirming the original order by the Illinois Commission, which was approved by the Illinois Commission on March 23, 2016 and concluded this matter. The Illinois Commission approved the purchase gas adjustments for the years 2004 through 2007 on August 9, 2016, and years 2008 and 2009 on August 24, 2016. As a condition of these approvals, Nicor Gas agreed to revise the way in which interest is reflected in the calculations beginning in 2013. Southern Company Gas does not expect this to have material impact on its consolidated financial statements. The gas cost prudence reviews for years 2010 through 2015 are underway. The ultimate outcome of these matters cannot be determined at this time.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS As of September 30, 2016 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using (a) (b) Successor – As of September 30, 2016 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient (NAV) Total (in millions) Assets: Energy-related derivatives $ 203 $ 162 $ — $ — $ 365 Total $ 203 $ 162 $ — $ — $ 365 Liabilities: Energy-related derivatives $ 267 $ 162 $ — $ — $ 429 Total $ 267 $ 162 $ — $ — $ 429 (a) Excludes $7 million associated with certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $111 million at September 30, 2016 . Valuation Methodologies The energy-related derivatives primarily consist of exchange-traded and non-exchange-traded derivatives such as over-the-counter forwards and options. These are standard products used within the energy industry and are valued using the market approach. The inputs used are mainly from observable market sources, such as forward natural gas prices and implied volatility. See Note (H) for additional information on how these derivatives are used. As of September 30, 2016 , other financial instruments for which the carrying amount did not equal fair value were as follows: Successor Carrying Amount Fair Value (in millions) Long-term debt, including securities due within one year $ 5,414 $ 5,383 The fair values are determined using Level 2 measurements and are based on quoted market prices for the same or similar issues or on the current rates available to Southern Company Gas.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Stockholders' Equity	STOCKHOLDERS' EQUITY Earnings per Share Upon consummation of the Merger, all of Southern Company Gas' shares are held by Southern Company. As a result, earnings per common share disclosures are no longer required. See Note (I) for additional information regarding the Merger. Changes in Stockholders' Equity Number of Common Stockholders' Equity Noncontrolling Interest Total Stockholders' Equity Issued Treasury (in thousands) (in millions) Predecessor – Balance at December 31, 2015 120,377 217 $ 3,929 $ 46 $ 3,975 Consolidated net income attributable to Southern Company Gas — — 131 — 131 Other comprehensive income (loss) — — (35 ) — (35 ) Stock issued 95 — 6 — 6 Stock-based compensation 270 — 30 — 30 Cash dividends on common stock — — (128 ) — (128 ) Reclassification of noncontrolling interest (*) — — — (46 ) (46 ) Predecessor – Balance at June 30, 2016 120,742 217 $ 3,933 $ — $ 3,933 Successor – Balance at July 1, 2016 — — $ 8,001 $ — $ 8,001 Consolidated net income attributable to Southern Company Gas — — 4 — 4 Capital contributions from parent company — — 1,089 — 1,089 Other comprehensive income (loss) — — (3 ) — (3 ) Stock-based compensation — — 7 — 7 Cash dividends on common stock — — (63 ) — (63 ) Successor – Balance at September 30, 2016 — — $ 9,035 $ — $ 9,035 Predecessor – Balance at December 31, 2014 119,647 217 $ 3,784 $ 44 $ 3,828 Consolidated net income attributable to Southern Company Gas — — 246 — 246 Other comprehensive income (loss) — — 11 — 11 Stock issued 173 — 9 — 9 Stock-based compensation 429 — 2 — 2 Cash dividends on common stock — — (183 ) — (183 ) Distribution to noncontrolling interest — — — (18 ) (18 ) Net income attributable to noncontrolling interest (*) — — — 15 15 Predecessor – Balance at September 30, 2015 120,249 217 $ 3,869 $ 41 $ 3,910 (*) Associated with SouthStar. See Note (K) for additional information.

Financing

Financing	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Financing	FINANCING Bank Credit Arrangements Bank credit arrangements under the Southern Company Gas Credit Facility and the Nicor Gas Credit Facility provide liquidity support to Southern Company Gas Capital's and Nicor Gas' commercial paper borrowings. The Nicor Gas Credit Facility is restricted for working capital needs of Nicor Gas. See Note 9 to the consolidated financial statements under "Short-term Debt" of Southern Company Gas in Item 8 of the Form 10-K and "Financing Activities" herein for additional information. The following table outlines the committed credit arrangements by company as of September 30, 2016 : Successor Expires Company 2017 2018 Total Unused (in millions) (in millions) Southern Company Gas Capital $ 49 $ 1,251 $ 1,300 $ 1,247 Nicor Gas 26 674 700 700 Total $ 75 $ 1,925 $ 2,000 $ 1,947 Additionally, Pivotal Utility Holdings is party to a series of loan agreements with the New Jersey Economic Development Authority and Brevard County, Florida under which five series of gas facility revenue bonds have been issued totaling $200 million . Subject to applicable market conditions, Southern Company Gas Capital and Nicor Gas expect to renew or replace their bank credit arrangements as needed, prior to expiration. In connection therewith, they may extend the maturity dates and/or increase or decrease the lending commitments thereunder. Financing Activities Southern Company Gas fully and unconditionally guarantees all debt issued by Southern Company Gas Capital and the gas facility revenue bonds issued by Pivotal Utility Holdings. Substantially all of Nicor Gas' properties are subject to the lien of the indenture securing its first mortgage bonds. In February and May 2016, $75 million and $50 million , respectively, of Nicor Gas' first mortgage bonds matured and were repaid using the proceeds from commercial paper borrowings. In June 2016, Nicor Gas issued $250 million aggregate principal amount of first mortgage bonds with the following terms: $100 million at 2.66% due June 20, 2026, $100 million at 2.91% due June 20, 2031, and $50 million at 3.27% due June 20, 2036. The proceeds were used to repay short-term indebtedness incurred under the Nicor Gas commercial paper program and for other working capital needs. In May 2016, Southern Company Gas Capital issued $350 million aggregate principal amount of 3.250% Senior Notes due June 15, 2026, which are guaranteed by Southern Company Gas. A portion of the proceeds were used to repay at maturity $300 million aggregate principal amount of 6.375% Senior Notes due July 15, 2016, and the remaining proceeds were used for general corporate purposes. In September 2016, Southern Company Gas Capital issued $350 million aggregate principal amount of 2.45% Senior Notes due October 1, 2023 and $550 million aggregate principal amount of 3.95% Senior Notes due October 1, 2046, both of which are guaranteed by Southern Company Gas. The proceeds were used to repay a $360 million promissory note issued to Southern Company for the purpose of funding a portion of the purchase price for Southern Company Gas' 50% equity interest in SNG, to fund the purchase of Piedmont's interest in SouthStar, to make a voluntary pension contribution, to repay at maturity $120 million aggregate principal amount of Series A Floating Rate Senior Notes due October 27, 2016, and for general corporate purposes. See Note (I) under " Investment in SNG " for additional information on the SNG investment and Note (K) under "Subsequent Event" for additional information on GNG's acquisition of Piedmont's interest in SouthStar. Certain of Southern Company Gas' senior notes with a principal amount of $275 million were subject to change in control provisions that were triggered by the Merger. Under the applicable Note Purchase Agreement, Southern Company Gas Capital was required to provide notice to the holders of these notes of the change in control and offer to prepay these notes in August 2016. None of the holders of these notes accepted the offer for prepayment. These senior notes, which were recorded as current portion of long-term debt as of June 30, 2016 and include $120 million due October 27, 2016 and $155 million due October 27, 2018, will remain on their original payment schedules and the portion related to the notes due in 2018 has been reclassified to long-term debt in the balance sheet as of September 30, 2016 .

Retirement Benefits

Retirement Benefits	9 Months Ended
	Sep. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Retirement Benefits	RETIREMENT BENEFITS Effective July 1, 2016, in connection with the Merger, Southern Company Services, Inc. became the sponsor of Southern Company Gas' pension and other postretirement benefit plans. Southern Company Gas has a defined benefit, trusteed, pension plan – AGL Resources Inc. Retirement Plan – covering eligible employees. The qualified pension plan is funded in accordance with requirements of the Employee Retirement Income Security Act of 1974, as amended. Southern Company Gas made a $125 million voluntary contribution to the qualified pension plan in September 2016. No mandatory contributions to the qualified pension plan are anticipated for the year ending December 31, 2016 . Southern Company Gas also provides certain defined benefit and defined contribution plans for a selected group of management and highly compensated employees. Benefits under these non-qualified plans are largely unfunded and benefits are primarily paid using corporate assets. In addition, Southern Company Gas provides certain medical care and life insurance benefits for eligible retired employees through a postretirement benefit plan – AGL Welfare Plan. Southern Company Gas also has a separate unfunded supplemental retirement health care plan that provides medical care and life insurance benefits to employees of discontinued businesses. See Note 7 to the consolidated financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional information on Southern Company Gas' retirement benefit plans. In connection with the Merger, Southern Company Gas performed updated valuations of its pension and other postretirement benefit plan assets and obligations to reflect actual census data at the new measurement date of July 1, 2016. This valuation resulted in increases to the projected benefit obligations for the pension and other postretirement benefit plans of approximately $177 million and $20 million , respectively, a decrease in the fair value of pension plan assets of $10 million , and an increase in the fair value of other postretirement benefit plan assets of $1 million . Southern Company Gas also recorded a related regulatory asset of $437 million related to unrecognized prior service cost and actuarial gain/loss, as it is probable that this amount will be recovered through future rates for Southern Company Gas' regulated utilities. The previously unrecognized prior service cost and actuarial gain/loss related to non-utility subsidiaries were eliminated through purchase accounting adjustments. Actuarial Assumptions The weighted average rates assumed in the actuarial calculations used to determine the net periodic costs for the pension and other postretirement benefit plans for the successor period ended September 30, 2016 and the benefit obligations as of the new measurement date, July 1, 2016, are presented below. Successor Predecessor Assumptions used to determine net periodic costs: July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 For the Three and Nine Months Ended September 30, 2015 Pension plans Discount rate – interest costs (a) 3.2 % 4.0 % 4.2 % Discount rate – service costs (a) 4.1 4.8 4.2 Expected long-term return on plan assets 7.8 7.8 7.8 Annual salary increase 3.5 3.7 3.7 Pension band increase (b) 2.0 2.0 2.0 Other postretirement benefit plans Discount rate – interest costs (a) 2.8 3.6 4.0 Discount rate – service costs (a) 4.0 4.7 4.0 Expected long-term return on plan assets 6.1 6.6 7.4 Annual salary increase 3.5 3.7 3.7 (a) Rates are presented on a weighted average basis for the three and nine months ended September 30, 2015. (b) Only applicable to the Nicor Gas union employees. The pension bands for the former Nicor plan have been updated to reflect the new negotiated rates for each of 2016 and 2017 of 2.0% , as indicated in the union agreement dated March 2014. Successor Predecessor Assumptions used to determine benefit obligations: July 1, 2016 December 31, 2015 Pension plans Discount rate 3.9 % 4.6 % Annual salary increase 3.5 3.7 Pension band increase (*) 2.0 2.0 Other postretirement benefit plans Discount rate 3.6 4.4 Annual salary increase 3.5 3.7 (*) Only applicable to the Nicor Gas union employees. The pension bands for the former Nicor plan have been updated to reflect the new negotiated rates for each of 2016 and 2017 of 2.0% , as indicated in the union agreement dated March 2014. An additional assumption used in measuring the accumulated other postretirement benefit obligations (APBO) is the weighted average medical care cost trend rate. The weighted average medical care cost trend rates used in measuring the APBO for the successor period ended September 30, 2016 as of the new measurement date, July 1, 2016, and for the predecessor period ended December 31, 2015 were as follows: Initial Cost Trend Rate Ultimate Cost Trend Rate Year That Ultimate Rate is Reached Successor – July 1, 2016 Pre-65 6.8 % 4.5 % 2038 Post-65 medical 8.8 4.5 2038 Post-65 prescription 8.8 4.5 2038 Predecessor – December 31, 2015 Pre-65 6.8 4.5 2038 Post-65 medical 8.8 4.5 2038 Post-65 prescription 8.8 4.5 2038 Components of the net periodic benefit costs for the periods presented were as follows: Pension Plan (in millions) Successor – July 1, 2016 through September 30, 2016 Service cost (a) $ 7 Interest cost (a) 10 Expected return on plan assets (17 ) Amortization of regulatory asset 6 Net periodic pension cost $ 6 Predecessor – January 1, 2016 through June 30, 2016 Service cost (a) $ 13 Interest cost (a) 21 Expected return on plan assets (33 ) Amortization: Prior service costs (1 ) Net (gain)/loss 13 Net periodic pension cost $ 13 Predecessor – Three Months Ended September 30, 2015 Service cost $ 7 Interest cost 11 Expected return on plan assets (16 ) Amortization: Prior service costs (1 ) Net (gain)/loss 8 Net periodic pension cost $ 9 Predecessor – Nine Months Ended September 30, 2015 Service cost $ 21 Interest cost 34 Expected return on plan assets (49 ) Amortization: Prior service costs (2 ) Net (gain)/loss 23 Net periodic pension cost $ 27 (a) Effective January 1, 2016, Southern Company Gas uses a spot rate approach to estimate the service cost and interest cost components. Historically, Southern Company Gas estimated these components using a single weighted-average discount rate. Postretirement Benefits (in millions) Successor – July 1, 2016 through September 30, 2016 Service cost (a) $ 1 Interest cost (a) 2 Expected return on plan assets (2 ) Amortization of regulatory asset 1 Net periodic postretirement benefit cost $ 2 Predecessor – January 1, 2016 through June 30, 2016 Service cost (a) $ 1 Interest cost (a) 5 Expected return on plan assets (3 ) Amortization: Prior service costs (1 ) Net (gain)/loss 2 Net periodic postretirement benefit cost $ 4 Predecessor – Three Months Ended September 30, 2015 Service cost $ — Interest cost 4 Expected return on plan assets (1 ) Amortization: Prior service costs (1 ) Net (gain)/loss 1 Net periodic postretirement benefit cost $ 3 Predecessor – Nine Months Ended September 30, 2015 Service cost $ 1 Interest cost 10 Expected return on plan assets (5 ) Amortization: Prior service costs (2 ) Net (gain)/loss 4 Net periodic postretirement benefit cost $ 8 (a) Effective January 1, 2016, Southern Company Gas uses a spot rate approach to estimate the service cost and interest cost components. Historically, Southern Company Gas estimated these components using a single weighted-average discount rate.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES See Note 13 to the consolidated financial statements of Southern Company Gas in Item 8 of the Form 10-K for additional tax information. Effective Tax Rate Southern Company Gas' effective tax rate was 59.6% for the successor period July 1, 2016 through September 30, 2016 and 37.6% for the predecessor period January 1, 2016 through June 30, 2016 , compared to 37.9% for the predecessor period nine months ended September 30, 2015 . The effective tax rates for the periods in 2016 were impacted by the nondeductibility of certain Merger-related expenses, which were re-assessed in the second and third quarters 2016. The effective tax rate for the successor period July 1, 2016 through September 30, 2016 was also impacted by nondeductible expenses associated with change in control compensation charges. Removing the impact of the Merger-related expenses, the effective tax rate for the predecessor period was 37.5% and for the successor period was 39.1% .

Derivatives

Derivatives	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	DERIVATIVES Southern Company Gas is exposed to market risks, primarily commodity price risk, interest rate risk, and weather risk. To manage the volatility attributable to these exposures, Southern Company Gas nets its exposures, where possible, to take advantage of natural offsets and enters into various derivative transactions for the remaining exposures pursuant to Southern Company Gas' policies in areas such as counterparty exposure and risk management practices. Southern Company Gas' policy is that derivatives are to be used primarily for hedging purposes and mandates strict adherence to all applicable risk management policies. Derivative positions are monitored using techniques including, but not limited to, market valuation, value at risk, stress testing, and sensitivity analysis. Derivative instruments are recognized at fair value in the balance sheets as either assets or liabilities and are presented on a net basis. See Note (C) for additional information. In the statements of cash flows, the cash impacts of settled energy-related and interest rate derivatives are recorded as operating activities. Energy-Related Derivatives Southern Company Gas enters into energy-related derivatives to hedge exposures to natural gas and other fuel price changes. However, due to cost-based rate regulations and other various cost recovery mechanisms, Southern Company Gas has limited exposure to market volatility in prices of natural gas. Southern Company Gas manages fuel-hedging programs, implemented per the guidelines of its respective state regulatory agencies, through the use of financial derivative contracts, which is expected to continue to mitigate price volatility. Southern Company Gas has limited exposure to market volatility in prices of natural gas because the long-term sales contracts shift substantially all fuel cost responsibility to the purchaser. However, Southern Company Gas may be exposed to market volatility in energy-related commodity prices to the extent any uncontracted capacity is used to sell natural gas. Energy-related derivative contracts are accounted for under one of three methods: • Regulatory Hedges — Energy-related derivative contracts which are designated as regulatory hedges relate primarily to Southern Company Gas' fuel-hedging programs, where gains and losses are initially recorded as regulatory liabilities and assets, respectively, and then are included in the cost of natural gas as the underlying natural gas is used in operations and ultimately recovered through the respective cost recovery clauses. • Cash Flow Hedges — Gains and losses on energy-related derivatives designated as cash flow hedges (which are mainly used to hedge anticipated purchases and sales) are initially deferred in other comprehensive income (OCI) before being recognized in the statements of income in the same period as the hedged transactions are reflected in earnings. • Not Designated — Gains and losses on energy-related derivative contracts that are not designated or fail to qualify as hedges are recognized in the statements of income in the period of change. Some energy-related derivative contracts require physical delivery as opposed to financial settlement, and this type of derivative is both common and prevalent within the natural gas industry. When an energy-related derivative contract is settled physically, any cumulative unrealized gain or loss is reversed and the contract price is recognized in the respective line item representing the actual price of the underlying goods being delivered. At September 30, 2016 , the net volume of energy-related derivative contracts for natural gas positions for Southern Company Gas, together with the longest hedge date over which it is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Successor Net Purchased/(Sold) mmBtu Longest Hedge Date Longest Non-hedge Date (in millions) 214 2018 2022 Southern Company Gas’ derivative instruments are comprised of both long and short natural gas positions. A long position is a contract to purchase natural gas, and a short position is a contract to sell natural gas. The volume presented above represents the net of long natural gas positions of 3.2 billion mmBtu and short natural gas positions ( 2.9 billion mmBtu) as of September 30, 2016 . For cash flow hedges, the amount to be reclassified from accumulated OCI to earnings for the next 12-month period ending September 30, 2017 is immaterial. Interest Rate Derivatives Southern Company Gas may also enter into interest rate derivatives to hedge exposure to changes in interest rates. The derivatives employed as hedging instruments are structured to minimize ineffectiveness. Derivatives related to existing variable rate securities or forecasted transactions are accounted for as cash flow hedges where the effective portion of the derivatives' fair value gains or losses is recorded in OCI and is reclassified into earnings at the same time the hedged transactions affect earnings, with any ineffectiveness recorded directly to earnings. Derivatives related to existing fixed rate securities are accounted for as fair value hedges, where the derivatives' fair value gains or losses and hedged items' fair value gains or losses are both recorded directly to earnings, providing an offset, with any difference representing ineffectiveness. Fair value gains or losses on derivatives that are not designated or fail to qualify as hedges are recognized in the statements of income as incurred. On January 23, 2015, Southern Company Gas executed $800 million in notional value of 10 -year and 30 -year fixed-rate forward-starting interest rate swaps to hedge potential interest rate volatility prior to its issuances of long-term debt in the fourth quarter 2015 and during 2016. Southern Company Gas designated the forward-starting interest rate swaps, which were settled in conjunction with the debt issuances, as cash flow hedges. Southern Company Gas settled $200 million of these interest rate swaps in November 2015 for an immaterial loss, $400 million upon pricing the first mortgage bonds in May 2016 at a loss of $26 million , and the remaining $200 million upon pricing the senior notes in September 2016 at a loss of $35 million . Due to the application of acquisition accounting, only $5 million of the pre-tax loss incurred and deferred in the successor period will be amortized to interest expense through 2046 and is immaterial on an annual basis. Derivative Financial Statement Presentation and Amounts The derivative contracts of Southern Company Gas are subject to master netting arrangements or similar agreements and are reported net on its financial statements. Some of these energy-related and interest rate derivative contracts may contain certain provisions that permit intra-contract netting of derivative receivables and payables for routine billing and offsets related to events of default and settlements. At September 30, 2016 and December 31, 2015 , the value of energy-related derivatives and interest rate derivatives was reflected in the balance sheets as follows: Asset Derivatives Liability Derivatives Successor Predecessor Successor Predecessor Derivative Category Balance Sheet Location September 30, 2016 December 31, 2015 Balance Sheet Location September 30, 2016 December 31, 2015 (in millions) (in millions) (in millions) (in millions) Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives Assets from risk management activities – current $ 8 $ 10 Liabilities from risk management activities – current $ (6 ) $ (28 ) Other deferred charges and assets — — Other deferred credits and liabilities — (2 ) Total derivatives designated as hedging instruments for regulatory purposes $ 8 $ 10 $ (6 ) $ (30 ) Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives Assets from risk management activities – current $ 2 $ 3 Liabilities from risk management activities – current $ (3 ) $ (5 ) Other deferred charges and assets — — Other deferred credits and liabilities (1 ) (2 ) Interest rate derivatives: Assets from risk management activities – current — 9 Liabilities from risk management activities – current — — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 2 $ 12 $ (4 ) $ (7 ) Derivatives not designated as hedging instruments Energy-related derivatives Assets from risk management activities – current $ 304 $ 741 Liabilities from risk management activities – current $ (345 ) $ (644 ) Other deferred charges and assets 58 179 Other deferred credits and liabilities (74 ) (185 ) Total derivatives not designated as hedging instruments $ 362 $ 920 $ (419 ) $ (829 ) Gross amount of recognized assets and liabilities (a) (b) $ 372 $ 942 $ (429 ) $ (866 ) Gross amounts offset in the balance sheet (b) (258 ) (724 ) 369 820 Net amounts of derivatives assets and liabilities, presented in the balance sheet (c) $ 114 $ 218 $ (60 ) $ (46 ) (a) The gross amounts of recognized assets and liabilities are netted on the consolidated balance sheets to the extent that there were netting arrangements with the counterparties. (b) The gross amounts of recognized assets and liabilities do not include cash collateral held on deposit in broker margin accounts of $111 million as of September 30, 2016 and $96 million as of December 31, 2015 . (c) As of September 30, 2016 and December 31, 2015, letters of credit from counterparties offset an immaterial portion of these assets under master netting arrangements. At September 30, 2016 and December 31, 2015 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Unrealized Losses Unrealized Gains Successor Predecessor Successor Predecessor Derivative Category Balance Sheet Location September 30, 2016 December 31, 2015 Balance Sheet Location September 30, 2016 December 31, 2015 (in millions) (in millions) (in millions) (in millions) Energy-related derivatives: Other regulatory assets, current $ (3 ) $ (15 ) Other regulatory liabilities, current $ 3 $ 15 Other regulatory assets, deferred — (2 ) Other regulatory liabilities, deferred — — Total energy-related derivative gains (losses) $ (3 ) $ (17 ) $ 3 $ 15 For the successor period July 1, 2016 through September 30, 2016 and the predecessor period three months ended September 30, 2015 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments recognized in OCI and those reclassified from accumulated OCI into earnings were as follows: Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Successor Predecessor Successor Predecessor Derivatives in Cash Flow Hedging Relationships July 1, 2016 through September 30, 2016 Three Months Ended September 30, 2015 Statements of Income Location July 1, 2016 through September 30, 2016 Three Months Ended September 30, 2015 (in millions) (in millions) (in millions) (in millions) Energy-related derivatives $ — $ (2 ) Cost of natural gas $ — $ (2 ) Interest rate derivatives (5 ) (46 ) Interest expense, net of amounts capitalized — 1 Total derivatives in cash flow hedging relationships $ (5 ) $ (48 ) $ — $ (1 ) For the predecessor periods January 1, 2016 through June 30, 2016 and nine months ended September 30, 2015 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments recognized in OCI and those reclassified from accumulated OCI into earnings were as follows: Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Predecessor Predecessor Derivatives in Cash Flow Hedging Relationships January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 Statements of Income Location January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 (in millions) (in millions) Energy-related derivatives $ — $ (3 ) Cost of natural gas $ (1 ) $ (6 ) Other operations and maintenance — (1 ) Interest rate derivatives (64 ) (1 ) Interest expense, net of amounts capitalized — 2 Total derivatives in cash flow hedging relationships $ (64 ) $ (4 ) $ (1 ) $ (5 ) For the successor period July 1, 2016 through September 30, 2016 and the predecessor periods January 1, 2016 through June 30, 2016 and three and nine months ended September 30, 2015 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments were as follows: Derivatives in Non-Designated Hedging Relationships Gain (Loss) Successor Predecessor Derivative Category Statements of Income Location July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 Three Months Ended September 30, 2015 Nine Months Ended September 30, 2015 (millions) (millions) Energy-related derivatives Natural gas revenues (*) $ — $ (1 ) $ 29 $ 7 Cost of natural gas 6 (62 ) 1 3 Total derivatives in non-designated hedging relationships $ 6 $ (63 ) $ 30 $ 10 (*) Excludes gains (losses) recorded in natural gas revenues associated with weather derivatives of $3 million for the predecessor period January 1, 2016 through June 30, 2016 and of $(1) million for the predecessor nine months ended September 30, 2015. There were no amounts recorded for the successor period July 1, 2016 through September 30, 2016 and the predecessor three months ended September 30, 2015. Contingent Features Southern Company Gas does not have any credit arrangements that would require material changes in payment schedules or terminations as a result of a credit rating downgrade. There are certain derivatives that could require collateral, but not accelerated payment, in the event of a credit rating change below BBB- and/or Baa3. At September 30, 2016 , Southern Company Gas had $111 million of collateral posted with derivative counterparties. At September 30, 2016 , the fair value of derivative liabilities with contingent features and the maximum potential collateral requirements arising from the credit-risk-related contingent features were immaterial. Generally, collateral may be provided by guaranty, letter of credit, or cash. If collateral is required, fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral are not offset against fair value amounts recognized for derivatives executed with the same counterparty. Southern Company Gas is exposed to losses related to financial instruments in the event of counterparties' nonperformance. Southern Company Gas only enters into agreements and material transactions with counterparties that have investment grade credit ratings by Moody's and S&P or with counterparties who have posted collateral to cover potential credit exposure. Southern Company Gas has also established risk management policies and controls to determine and monitor the creditworthiness of counterparties in order to mitigate Southern Company Gas' exposure to counterparty credit risk. Southern Company Gas also utilizes master netting agreements whenever possible to mitigate exposure to counterparty credit risk. When Southern Company Gas is engaged in more than one outstanding derivative transaction with the same counterparty and it also has a legally enforceable netting agreement with that counterparty, the "net" mark-to-market exposure represents the netting of the positive and negative exposures with that counterparty and a reasonable measure of Southern Company Gas' credit risk. Southern Company Gas also uses other netting agreements with certain counterparties with whom it conducts significant transactions. Master netting agreements enable Southern Company Gas to net certain assets and liabilities by counterparty. Southern Company Gas also nets across product lines and against cash collateral, provided the master netting and cash collateral agreements include such provisions. Southern Company Gas may require counterparties to pledge additional collateral when deemed necessary. Therefore, Southern Company Gas does not anticipate a material adverse effect on the financial statements as a result of counterparty nonperformance.

Merger and Acquisition

Merger and Acquisition	9 Months Ended
	Sep. 30, 2016
Business Combinations [Abstract]
Merger and Acquisition	MERGER AND ACQUISITION Merger with Southern Company On July 1, 2016, Southern Company Gas completed its previously announced Merger with Southern Company. A wholly-owned, direct subsidiary of Southern Company merged with and into Southern Company Gas, with Southern Company Gas surviving as a wholly-owned, direct subsidiary of Southern Company. At the effective time of the Merger, each share of Southern Company Gas common stock, other than certain excluded shares, was converted into the right to receive $66 in cash, without interest. Also at the effective time of the Merger: • Southern Company Gas' outstanding restricted stock units, restricted stock awards, and non-employee director stock awards were deemed fully vested and were canceled and converted into the right to receive an amount in cash equal to the product of (i) the total number of shares of Southern Company Gas' common stock subject to such award and (ii) the Merger consideration of $66 per share; • Southern Company Gas' outstanding stock options, all of which were fully vested, were canceled and converted into the right to receive an amount in cash equal to the product of (i) the total number of shares of Southern Company Gas' common stock subject to such options and (ii) the excess of the Merger consideration of $66 per share over the applicable exercise price per share of such options; and • each outstanding award of performance share units was converted into an award of Southern Company's restricted stock units. The conversion ratio was the product of (i) the greater of (a) 125% of the number of units underlying such award based on target level achievement of all relevant performance goals and (b) the number of units underlying such award based on the actual level of achievement of all relevant performance goals against target and (ii) an exchange ratio based on the Merger consideration of $66 per share as compared to the volume-weighted average price per share of Southern Company common stock, on the same terms and conditions relating to vesting schedule and payment terms, and otherwise on similar terms and conditions, as were applicable to such performance share unit awards, subject to certain exceptions. The application of the acquisition method of accounting was pushed down to Southern Company Gas. The excess of the purchase price over the fair values of Southern Company Gas' assets and liabilities was recorded as goodwill, which represents a different basis of accounting from the historical basis prior to the Merger. The following table presents the preliminary purchase price allocation: Successor Predecessor New Basis Old Basis Change in Basis (in millions) (in millions) Current assets $ 1,557 $ 1,474 $ 83 Property, plant, and equipment 10,108 10,148 (40 ) Goodwill 5,937 1,813 4,124 Other intangible assets 400 101 299 Regulatory assets 1,118 679 439 Other assets 229 273 (44 ) Current liabilities (2,201 ) (2,205 ) 4 Other liabilities (4,712 ) (4,600 ) (112 ) Long-term debt (4,261 ) (3,709 ) (552 ) Contingently redeemable noncontrolling interest (174 ) (41 ) (133 ) Total purchase price/equity $ 8,001 $ 3,933 $ 4,068 The estimated fair values noted above for the new basis are preliminary and are subject to change upon finalization of the purchase accounting assessment as additional information related to the fair value of assets and liabilities becomes available. Subsequent adjustments to the preliminary purchase price allocation are not expected to have a material impact on the results of operations and financial position of Southern Company Gas. In determining the fair value of assets and liabilities subject to rate regulation that allows recovery of costs and/or a fair return on investments, historical cost was deemed to be a reasonable proxy for fair value, as it is included in rate base or otherwise specified in regulatory recovery mechanisms. Property, plant, and equipment subject to rate regulation was reflected based on the historical gross amount of assets in service and accumulated depreciation, as they are included in rate base. For certain assets and liabilities subject to rate regulation (such as debt instruments and employee benefit obligations), the fair value adjustment was applied to historical cost with a corresponding offset to regulatory asset or liability based on the assessment of probable future recovery in rates. For unregulated assets and liabilities, fair value adjustments were applied to historical cost of natural gas for sale, property, plant, and equipment, debt instruments, and noncontrolling interest. The valuation of other intangible assets included customer relationships, trade names, and favorable/unfavorable contracts. The valuation of these assets and liabilities applied either the market approach or income approach. The market approach was utilized when prices and other relevant market information were available. The income approach, which is based on discounted cash flows, was primarily based on significant unobservable inputs (Level 3). Key estimates and inputs included forecasted profitability and cash flows, customer retention rates, royalty rates, and discount rates. The estimated fair value of deferred income taxes was determined by applying the appropriate enacted statutory tax rate to the temporary differences that arose on the differences between the financial reporting value and tax basis of the assets acquired and liabilities assumed. The excess of the purchase price over the estimated fair value of assets and liabilities of $5.9 billion was recognized as goodwill, which is primarily attributable to positioning Southern Company to provide natural gas infrastructure to meet customers' growing energy needs and to compete for growth across the energy value chain. Southern Company Gas anticipates that the majority of the value assigned to goodwill will not be deductible for tax purposes. Southern Company Gas' results for the successor period July 1, 2016 through September 30, 2016 include a $28 million ( $17 million , net of tax) decrease in consolidated net income primarily comprised of $29 million of reduced revenues and $11 million of increased amortization expense, partially offset by lower interest expense of $10 million as a result of the pushdown of acquisition accounting to reflect the fair values of assets and liabilities. During the successor period July 1, 2016 through September 30, 2016 , Southern Company Gas recorded in its statements of income transaction costs associated with the Merger of $35 million ( $24 million , net of tax). Transaction costs included $18 million in rate credits provided to Elizabethtown Gas customers as a condition of the Merger, $2 million for financial advisory fees, legal expenses, and other Merger-related costs, including certain amounts payable upon successful completion of the Merger, and $15 million for additional compensation related expenses, including accelerated vesting of share-based compensation expenses and change in control compensation charges. During the predecessor period January 1, 2016 through June 30, 2016 , Southern Company Gas recorded in its statements of income transaction costs of $56 million ( $41 million , net of tax). Transaction costs included $31 million for financial advisory fees, legal expenses, and other Merger-related costs, including certain amounts payable upon successful completion of the Merger, which was deemed probable on June 29, 2016, and $25 million of additional compensation related expenses, including accelerated vesting of share-based compensation expenses and certain Merger-related compensation charges. Southern Company Gas recorded Merger-related expenses of $35 million ( $21 million , net of tax) for both the predecessor three and nine months ended September 30, 2015 . Southern Company Gas previously treated these costs as tax deductible since the requisite closing conditions to the Merger had not yet been satisfied. During the second quarter 2016, when the Merger became probable, Southern Company Gas re-evaluated the tax deductibility of these costs and reflected any non-deductible amounts in the effective tax rate. The receipt of required regulatory approvals was conditioned upon certain terms and commitments. In connection with these regulatory approvals, certain regulatory agencies prohibited Southern Company Gas from recovering goodwill and Merger-related expenses, required Southern Company Gas to maintain a minimum number of employees for a set period of time to ensure that certain pipeline safety standards and the competence level of the employee workforce is not degraded, and/or required Southern Company Gas to maintain its pre-Merger level of support for various social and charitable programs. The most notable terms and commitments with potential financial impacts included: • rate credits of $18 million to be paid to customers in New Jersey and Maryland; • sharing of Merger savings with customers in Georgia starting in 2020; • phasing-out the use of the Nicor name or logo by Southern Company Gas' gas marketing services subsidiaries in conducting non-utility business in Illinois; • reaffirming that Elizabethtown Gas would file a base rate case no later than September 1, 2016, with another base rate case no later than three years after the 2016 rate case; and • requiring Elkton Gas to file a base rate case within 2 years of closing the Merger. There is no restriction on Southern Company Gas' other utilities' ability to file future rate cases. The rate credits to customers in New Jersey were paid during the third quarter 2016 and Elizabethtown Gas filed a base rate case with the New Jersey BPU on September 1, 2016. Upon completion of the Merger, Southern Company Gas amended and restated its Bylaws and Articles of Incorporation, under which it now has the authority to issue no more than 110 million shares of stock consisting of (i) 100 million shares of common stock and (ii) 10 million shares of preferred stock, both categories of which have a par value of $0.01 per share. The amended and restated Articles of Incorporation do not allow any treasury shares to be held. Investment in SNG On September 1, 2016, Southern Company Gas, through a wholly-owned, indirect subsidiary, acquired a 50% equity interest in SNG pursuant to a definitive agreement between Southern Company and Kinder Morgan, Inc. on July 10, 2016, to which Southern Company assigned all rights and obligations to Southern Company Gas on August 31, 2016. SNG owns a 7,000 -mile pipeline system connecting natural gas supply basins in Texas, Louisiana, Mississippi, and Alabama to markets in Louisiana, Mississippi, Alabama, Florida, Georgia, South Carolina, and Tennessee. The purchase price of $1.4 billion was financed by a $1.05 billion equity contribution from Southern Company and $360 million of cash paid by Southern Company Gas, which was financed by a bridge loan from Southern Company and repaid with a portion of the proceeds from the debt Southern Company Gas issued in September 2016. The purchase price of the 50% equity interest exceeded the underlying ownership interest in the net assets of SNG by approximately $700 million . This basis difference is attributable to goodwill and deferred tax assets. While the deferred tax assets will be amortized through deferred tax expense, the goodwill will not be amortized and is not required to be tested for impairment on an annual basis. See Note (K) under "Equity Method Investments" for additional information on this investment. Prior to Southern Company Gas’ completion of its acquisition of a 50% equity interest in SNG, Southern Company Gas had entered into long-term interstate natural gas transportation agreements with SNG. The interstate transportation service provided by SNG pursuant to these agreements is governed by the terms and conditions of SNG’s natural gas tariff and is subject to FERC regulation. For the period subsequent to acquisition, transportation costs paid to SNG by Southern Company Gas were approximately $4 million .

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Segment and Related Information	SEGMENT AND RELATED INFORMATION Southern Company Gas manages its business through four reportable segments – gas distribution operations (formerly referred to as distribution operations), gas marketing services (formerly referred to as retail operations), wholesale gas services (formerly referred to as wholesale services), and gas midstream operations (formerly referred to as midstream operations). The non-reportable segments are combined and presented as "all other." In conjunction with the Merger, Southern Company Gas changed the names of certain reportable segments to better align with its new parent company. The gas distribution operations segment is the largest component of Southern Company Gas' business and includes natural gas local distribution utilities that construct, manage, and maintain intrastate natural gas pipelines and gas distribution facilities in seven states. The gas marketing services segment includes natural gas marketing to end-use customers primarily in Georgia and Illinois. Additionally, gas marketing services provides home equipment protection products and services. The wholesale gas services segment provides natural gas asset management and/or related logistics services for each of Southern Company Gas' utilities except Nicor Gas as well as for non-affiliated companies. Additionally, this segment engages in natural gas storage and gas pipeline arbitrage and related activities. The gas midstream operations segment includes Southern Company Gas' non-utility pipeline and storage operations. The "all other" column includes segments below the quantitative threshold for separate disclosure. These segments include subsidiaries that do not align with one of Southern Company Gas' reportable segments. The chief operating decision maker of Southern Company Gas is the Chairman, President, and Chief Executive Officer, who utilizes earnings before interest and taxes (EBIT) as the primary measure of profit and loss in assessing the results of each segment’s operations. EBIT includes operating income and other income and (expense) and excludes interest expense, net of amounts capitalized and income taxes, which are evaluated on a consolidated basis. Business segment financial data for the successor period July 1, 2016 through September 30, 2016 and the predecessor periods January 1, 2016 through June 30, 2016 and three and nine months ended September 30, 2015 was as follows: Gas distribution operations Gas marketing services Wholesale gas services (*) Gas midstream operations All other Intercompany eliminations Consolidated (in millions) Successor – July 1, 2016 through September 30, 2016 Operating revenues $ 455 $ 126 $ (8 ) $ 13 $ 2 $ (45 ) $ 543 EBIT 75 (6 ) (17 ) 25 (27 ) — 50 Segment net income (loss) 27 (4 ) (11 ) 14 (22 ) — 4 Capital expenditures 268 3 1 19 7 — 298 Successor – Total assets at September 30, 2016 $ 16,184 $ 1,991 $ 1,007 $ 2,165 $ 10,274 $ (10,436 ) $ 21,185 (in millions) Predecessor – January 1, 2016 through June 30, 2016 Operating revenues $ 1,575 $ 435 $ (32 ) $ 25 $ 4 $ (102 ) $ 1,905 EBIT 353 109 (68 ) (6 ) (60 ) — 328 Segment net income (loss) 178 58 (42 ) (4 ) (59 ) — 131 Capital expenditures 484 4 1 43 16 — 548 Predecessor – Three Months Ended September 30, 2015 Operating revenues $ 445 $ 134 $ 34 $ 12 $ — $ (41 ) $ 584 EBIT 86 11 18 (16 ) (37 ) — 62 Segment net income (loss) 34 9 11 (9 ) (34 ) — 11 Capital expenditures 273 2 1 8 9 — 293 Predecessor – Nine Months Ended September 30, 2015 Operating revenues $ 2,332 $ 628 $ 128 $ 42 $ 9 $ (160 ) $ 2,979 EBIT 420 115 66 (20 ) (41 ) — 540 Segment net income (loss) 202 65 40 (12 ) (49 ) — 246 Capital expenditures 691 6 2 18 28 — 745 Predecessor – Total assets at December 31, 2015 $ 12,517 $ 686 $ 935 $ 692 $ 9,664 $ (9,740 ) $ 14,754 (*) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Wholesale gas services Third party gross revenues Intercompany revenues Total gross Less gross Operating (in millions) Successor – July 1, 2016 through September 30, 2016 $ 1,688 77 1,765 1,773 $ (8 ) Predecessor – (in millions) January 1, 2016 through June 30, 2016 $ 2,500 143 2,643 2,675 $ (32 ) Three months ended September 30, 2015 $ 1,440 90 1,530 1,496 $ 34 Nine months ended September 30, 2015 $ 4,876 329 5,205 5,077 $ 128

Non-Wholly Owned Entities and R

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest	9 Months Ended
	Sep. 30, 2016
Equity Method Investments and Joint Ventures [Abstract]
Non-Wholly Owned Entities and Redeemable Noncontrolling Interest	NON-WHOLLY-OWNED ENTITIES AND REDEEMABLE NONCONTROLLING INTEREST SouthStar, a joint venture owned by Southern Company Gas and Piedmont as of September 30, 2016 , is the only VIE for which Southern Company Gas is the primary beneficiary. See Note 11 to the consolidated financial statements under "Variable Interest Entities" of Southern Company Gas in Item 8 of the Form 10-K for additional information. In December 2015, GNG, a wholly-owned, direct subsidiary of Southern Company Gas, notified Piedmont of its election, pursuant to change in control provisions in the Second Amended and Restated Limited Liability Company Agreement of SouthStar, dated September 6, 2013, to purchase Piedmont’s 15% interest in SouthStar at fair market value. This purchase was contingent upon the closing of the merger between Piedmont and Duke Energy Corporation (Duke Energy). On February 12, 2016, GNG and Piedmont entered into a letter agreement pursuant to which GNG agreed to pay Piedmont $160 million as the fair value for Piedmont's entire ownership interest in SouthStar. After Piedmont and Duke Energy obtained the necessary regulatory approval for their merger in September 2016 and completed their merger in October 2016, GNG completed its purchase of Piedmont's interest in SouthStar on October 3, 2016. During the first quarter 2016, Southern Company Gas reclassified its noncontrolling interest related to Piedmont's 15% interest in SouthStar, whose redemption was beyond the control of Southern Company Gas, as a contingently redeemable noncontrolling interest. Upon Piedmont and Duke Energy obtaining the necessary merger approval, Southern Company Gas deemed its noncontrolling interest to be mandatorily redeemable and reclassified the noncontrolling interest to a current liability as of September 30, 2016 . The roll-forwards of the redeemable noncontrolling interest for the successor period July 1, 2016 through September 30, 2016 and the predecessor period January 1, 2016 through June 30, 2016 are detailed below: Predecessor – (in millions) Balance at December 31, 2015 $ — Reclassification of noncontrolling interest to contingently redeemable noncontrolling interest 46 Net income attributable to noncontrolling interest 14 Distribution to noncontrolling interest (19 ) Balance at June 30, 2016 $ 41 Successor – (in millions) Balance at July 1, 2016 $ 174 Reclassification of noncontrolling interest to mandatorily redeemable noncontrolling interest (174 ) Balance at September 30, 2016 $ — Southern Company Gas' cash flows used for investing activities include capital expenditures for SouthStar of $1 million for the successor period July 1, 2016 through September 30, 2016 , $2 million for the predecessor period January 1, 2016 through June 30, 2016 , and $3 million for the predecessor nine months ended September 30, 2015 . Southern Company Gas' cash flows used for financing activities include SouthStar’s distribution to Piedmont for its portion of SouthStar’s annual earnings from the previous year, which generally occurs in the first quarter of each fiscal year. No distributions were made for the successor period July 1, 2016 through September 30, 2016 ; however, see " Subsequent Event " herein for disclosure of a distribution made upon completion of the purchase of Piedmont's interest in SouthStar. For the predecessor periods January 1, 2016 through June 30, 2016 and the nine months ended September 30, 2015 , SouthStar distributed $19 million and $18 million , respectively, to Piedmont. SouthStar’s counterparties have no recourse to the general credit of Southern Company Gas beyond Southern Company Gas' corporate guarantees that were provided to SouthStar’s counterparties and natural gas suppliers. The following table provides additional information on SouthStar’s assets and liabilities as of the dates presented. The SouthStar amounts exclude intercompany eliminations and the balances of Southern Company Gas' wholly-owned, direct subsidiary with an 85% ownership interest in SouthStar. September 30, 2016 December 31, 2015 Successor Predecessor Consolidated SouthStar % Consolidated SouthStar % (in millions) (in millions) Current assets $ 1,759 $ 210 12 % $ 2,115 $ 245 12 % Goodwill and other intangible assets 6,317 110 2 1,922 114 6 Deferred charges and other assets 13,109 17 — 10,717 16 — Total Assets $ 21,185 $ 337 2 % $ 14,754 $ 375 3 % Current liabilities $ 2,321 $ 46 2 % $ 2,918 $ 54 2 % Deferred credits and other liabilities 9,829 1 — 7,861 — — Total Liabilities 12,150 47 — 10,779 54 1 Total Stockholders' Equity 9,035 290 3 3,975 321 8 Total Liabilities and Stockholders' Equity $ 21,185 $ 337 2 % $ 14,754 $ 375 3 % The following table provides information on SouthStar’s operating revenues and operating expenses for the periods presented, which are consolidated within Southern Company Gas' statements of income. Successor Predecessor Successor Predecessor Three Months Ended September 30, 2016 Three Months Ended September 30, 2015 July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 (in millions) (in millions) (in millions) (in millions) Total operating revenues $ 100 $ 103 $ 100 $ 372 $ 536 Operating Expenses: Cost of natural gas 77 78 77 234 370 Other operations and maintenance 18 18 18 40 59 Depreciation and amortization 3 2 3 4 7 Taxes other than income taxes — — — 1 1 Total operating expenses 98 98 98 279 437 Operating Income $ 2 $ 5 $ 2 $ 93 $ 99 Equity Method Investments See Note 11 to the consolidated financial statements of Southern Company Gas under "Equity Method Investments" in Item 8 of the Form 10-K for additional information. On September 1, 2016, Southern Company Gas, through a wholly-owned, indirect subsidiary, acquired a 50% equity interest in SNG, which is accounted for as an equity method investment. See Note (I) under " Investment in SNG " for additional information. Southern Company Gas determined that for the successor period July 1, 2016 through September 30, 2016 , SNG met the conditions of a significant subsidiary under SEC Regulation S-X Rule 3-09 and Regulation S-X Rule 4-08(g). Accordingly, summarized income statement information for SNG is presented below. Successor SNG September 1, 2016 through September 30, 2016 (in millions) Revenues $ 82 Operating income 60 Net income $ 55 Balance Sheet Information The carrying amounts within Southern Company Gas' balance sheets of its investments that are accounted for using the equity method were as follows: Successor Predecessor September 30, 2016 December 31, 2015 (in millions) (in millions) SNG $ 1,414 $ — Triton 45 49 Horizon Pipeline 31 14 Atlantic Coast Pipeline 23 7 PennEast Pipeline 17 9 Other 1 1 Total $ 1,531 $ 80 Income Statement Information The following table provides the income from equity method investments as recorded on Southern Company Gas' statements of income for the periods presented. Successor Predecessor Successor Predecessor Three Months Ended September 30, 2016 Three Months Ended September 30, 2015 July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 (in millions) (in millions) (in millions) (in millions) SNG $ 27 $ — $ 27 $ — $ — Triton 1 2 1 1 3 Atlantic Coast Pipeline 1 — 1 — — Horizon Pipeline — — — 1 1 Total $ 29 $ 2 $ 29 $ 2 $ 4 Subsequent Event Upon completion of the merger between Piedmont and Duke Energy on October 3, 2016, GNG completed its acquisition of Piedmont's 15% interest in SouthStar for a purchase price of $160 million . Additionally, $14 million was paid to Piedmont for its share of SouthStar's 2016 earnings through the date of acquisition. The purchase price and additional payout was funded through debt proceeds and was recorded in the consolidated balance sheet as a current liability at September 30, 2016.

Introduction (Policies)

Introduction (Policies)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Basis of Accounting	Southern Company Gas (formerly known as AGL Resources Inc.) is an energy services holding company whose primary business is the distribution of natural gas through natural gas distribution utilities. On July 1, 2016, Southern Company and Southern Company Gas completed the Merger and Southern Company Gas became a wholly-owned, direct subsidiary of Southern Company and, on July 11, 2016, changed its name to Southern Company Gas. See Note (I) for additional information regarding the Merger. The condensed consolidated quarterly financial statements included herein have been prepared, without audit, pursuant to the rules and regulations of the SEC. The condensed consolidated balance sheet as of December 31, 2015 has been derived from the audited consolidated financial statements of Southern Company Gas. In the opinion of management, the information furnished herein reflects all adjustments, which, except as otherwise disclosed, are of a normal recurring nature, necessary to present fairly the results of operations for the periods ended September 30, 2016 and 2015 . Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations, although Southern Company Gas believes that the disclosures are adequate to make the information presented not misleading. Disclosures which would substantially duplicate the disclosures in the Form 10-K and details which have not changed significantly in amount or composition since the filing of the Form 10-K are generally omitted from this Quarterly Report on Form 10-Q unless specifically required by GAAP. Therefore, these Condensed Consolidated Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K. Due to the seasonal variations in the demand for natural gas, operating results for the periods presented are not necessarily indicative of the operating results to be expected for the full year. Pursuant to the Merger, Southern Company has pushed down the application of the acquisition method of accounting to the consolidated financial statements of Southern Company Gas such that the assets and liabilities of Southern Company Gas are recorded at their respective fair values, and goodwill has been established for the excess of the purchase price over the fair value of net identifiable assets. Accordingly, the consolidated financial statements of Southern Company Gas for periods before and after July 1, 2016 (acquisition date) reflect different bases of accounting, and the financial positions and results of operations of those periods are not comparable. Throughout the consolidated financial statements and notes to those financial statements, periods prior to July 1, 2016 are identified as "predecessor," while periods after the acquisition date are identified as "successor." Certain prior year data and current year predecessor period data presented in the financial statements have been modified or reclassified to conform to the presentation used by Southern Company Gas’ new parent company, Southern Company. Changes to the consolidated statements of income include classifying operating revenues as natural gas revenues and other revenues as well as classifying cost of goods sold as cost of natural gas and cost of other sales, and presenting interest expense and allowance for equity funds used during construction on a gross basis. Changes to the consolidated statements of cash flows include revised financial statement line item descriptions to align with the new balance sheet descriptions and expanded line items within each type of cash flow activity. Changes to the consolidated balance sheets include changing certain captions to conform to the presentation of Southern Company. Such reclassification did not have a significant impact on the results of operations, financial position, or cash flows of Southern Company Gas.
Recently Issued Accounting Standards	Recently Issued Accounting Standards On November 20, 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes (ASU 2015-17), which simplifies the presentation of deferred income taxes. ASU 2015-17 requires deferred tax assets and liabilities to be presented as non-current in a classified balance sheet and is effective for fiscal years beginning after December 15, 2016, including interim periods within that reporting period. As permitted, Southern Company Gas elected to early adopt the guidance as of September 30, 2016 and applied its provisions retrospectively to each prior period presented for comparative purposes. Prior to the adoption of ASU 2015-17, all deferred income tax assets and liabilities were required to be separated into current and non-current amounts. The new guidance resulted in a reclassification of $31 million deferred income taxes, current to non-current accumulated deferred income taxes in Southern Company Gas' December 31, 2015 balance sheet. Other than the reclassification, the adoption of ASU 2015-17 did not have an impact on the results of operations, financial position, or cash flows of Southern Company Gas. On February 25, 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires lessees to recognize on the balance sheet a lease liability and a right-of-use asset for all leases. ASU 2016-02 also changes the recognition, measurement, and presentation of expense associated with leases and provides clarification regarding the identification of certain components of contracts that would represent a lease. The accounting required by lessors is relatively unchanged. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. Southern Company Gas is currently evaluating the new standard and has not yet determined its ultimate impact; however, adoption of ASU 2016-02 is expected to have a significant impact on Southern Company Gas' balance sheet. On March 30, 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (ASU 2016-09). ASU 2016-09 changes the accounting for income taxes and the cash flow presentation for share-based payment award transactions. Most significantly, entities are required to recognize all excess tax benefits and deficiencies related to the exercise or vesting of stock compensation as income tax expense or benefit in the income statement. Southern Company Gas currently recognizes any excess tax benefits and deficiencies related to the exercise and vesting of stock compensation in additional paid-in capital. ASU 2016-09 is effective for fiscal years beginning after December 15, 2016. Early adoption is permitted and Southern Company Gas intends to adopt the ASU in the fourth quarter 2016. The adoption is not expected to have a material impact on the results of operations, financial position, or cash flows of Southern Company Gas.

Introduction (Tables)

Introduction (Tables)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Schedule of Intangible Assets and Goodwill	Goodwill and other intangible assets consisted of the following: Successor – At September 30, 2016 Estimated Useful Life Gross Carrying Amount Accumulated Amortization Other Intangible Assets, Net (in millions) Other intangible assets subject to amortization: Gas marketing services Customer relationships 11-14 years $ 221 $ (15 ) $ 206 Trade names 10-28 years 115 (1 ) 114 Wholesale gas services Storage and transportation contracts 1-5 years 64 (4 ) 60 Total other intangible assets subject to amortization $ 400 $ (20 ) $ 380 Goodwill: Gas distribution operations $ 4,672 $ — $ 4,672 Gas marketing services 1,265 — 1,265 Total goodwill $ 5,937 $ — $ 5,937
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Amortization expense for the years 2017-2021 associated with other intangible assets is expected to be as follows: Amortization Expense (in millions) 2017 $ 73 2018 58 2019 40 2020 28 2021 21

Contingencies and Regulatory 23

Contingencies and Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2016
Regulatory Asset Off Balance Sheet [Member]
Regulated Operations [Line Items]
Schedule of Regulatory Assets	These amounts will be recognized as revenues in Southern Company Gas' financial statements in the periods they are billable to customers. Successor Predecessor September 30, 2016 December 31, 2015 (in millions) (in millions) Atlanta Gas Light (*) $ 109 $ 103 Virginia Natural Gas 12 12 Elizabethtown Gas 6 4 Nicor Gas 3 3 Total $ 130 $ 122 (*) In October 2015, Atlanta Gas Light received an order from the Georgia PSC, which included a final determination of the true-up recovery related to the PRP that allows Atlanta Gas Light to recover $144 million of the $178 million of incurred and allowed costs that were deferred for future recovery.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2016
Long-term Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	As of September 30, 2016 , other financial instruments for which the carrying amount did not equal fair value were as follows: Successor Carrying Amount Fair Value (in millions) Long-term debt, including securities due within one year $ 5,414 $ 5,383
Natural Gas and Interest Rate Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	As of September 30, 2016 , assets and liabilities measured at fair value on a recurring basis during the period, together with their associated level of the fair value hierarchy, were as follows: Fair Value Measurements Using (a) (b) Successor – As of September 30, 2016 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Net Asset Value as a Practical Expedient (NAV) Total (in millions) Assets: Energy-related derivatives $ 203 $ 162 $ — $ — $ 365 Total $ 203 $ 162 $ — $ — $ 365 Liabilities: Energy-related derivatives $ 267 $ 162 $ — $ — $ 429 Total $ 267 $ 162 $ — $ — $ 429 (a) Excludes $7 million associated with certain weather derivatives accounted for based on intrinsic value rather than fair value. (b) Excludes cash collateral of $111 million at September 30, 2016 .

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Schedule of Stockholders Equity	Changes in Stockholders' Equity Number of Common Stockholders' Equity Noncontrolling Interest Total Stockholders' Equity Issued Treasury (in thousands) (in millions) Predecessor – Balance at December 31, 2015 120,377 217 $ 3,929 $ 46 $ 3,975 Consolidated net income attributable to Southern Company Gas — — 131 — 131 Other comprehensive income (loss) — — (35 ) — (35 ) Stock issued 95 — 6 — 6 Stock-based compensation 270 — 30 — 30 Cash dividends on common stock — — (128 ) — (128 ) Reclassification of noncontrolling interest (*) — — — (46 ) (46 ) Predecessor – Balance at June 30, 2016 120,742 217 $ 3,933 $ — $ 3,933 Successor – Balance at July 1, 2016 — — $ 8,001 $ — $ 8,001 Consolidated net income attributable to Southern Company Gas — — 4 — 4 Capital contributions from parent company — — 1,089 — 1,089 Other comprehensive income (loss) — — (3 ) — (3 ) Stock-based compensation — — 7 — 7 Cash dividends on common stock — — (63 ) — (63 ) Successor – Balance at September 30, 2016 — — $ 9,035 $ — $ 9,035 Predecessor – Balance at December 31, 2014 119,647 217 $ 3,784 $ 44 $ 3,828 Consolidated net income attributable to Southern Company Gas — — 246 — 246 Other comprehensive income (loss) — — 11 — 11 Stock issued 173 — 9 — 9 Stock-based compensation 429 — 2 — 2 Cash dividends on common stock — — (183 ) — (183 ) Distribution to noncontrolling interest — — — (18 ) (18 ) Net income attributable to noncontrolling interest (*) — — — 15 15 Predecessor – Balance at September 30, 2015 120,249 217 $ 3,869 $ 41 $ 3,910 (*) Associated with SouthStar. See Note (K) for additional information.

Financing (Tables)

Financing (Tables)	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Schedule of Line of Credit Facilities	The following table outlines the committed credit arrangements by company as of September 30, 2016 : Successor Expires Company 2017 2018 Total Unused (in millions) (in millions) Southern Company Gas Capital $ 49 $ 1,251 $ 1,300 $ 1,247 Nicor Gas 26 674 700 700 Total $ 75 $ 1,925 $ 2,000 $ 1,947

Retirement Benefits (Tables)

Retirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Schedule of Assumptions Used	The weighted average rates assumed in the actuarial calculations used to determine the net periodic costs for the pension and other postretirement benefit plans for the successor period ended September 30, 2016 and the benefit obligations as of the new measurement date, July 1, 2016, are presented below. Successor Predecessor Assumptions used to determine net periodic costs: July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 For the Three and Nine Months Ended September 30, 2015 Pension plans Discount rate – interest costs (a) 3.2 % 4.0 % 4.2 % Discount rate – service costs (a) 4.1 4.8 4.2 Expected long-term return on plan assets 7.8 7.8 7.8 Annual salary increase 3.5 3.7 3.7 Pension band increase (b) 2.0 2.0 2.0 Other postretirement benefit plans Discount rate – interest costs (a) 2.8 3.6 4.0 Discount rate – service costs (a) 4.0 4.7 4.0 Expected long-term return on plan assets 6.1 6.6 7.4 Annual salary increase 3.5 3.7 3.7 (a) Rates are presented on a weighted average basis for the three and nine months ended September 30, 2015. (b) Only applicable to the Nicor Gas union employees. The pension bands for the former Nicor plan have been updated to reflect the new negotiated rates for each of 2016 and 2017 of 2.0% , as indicated in the union agreement dated March 2014. Successor Predecessor Assumptions used to determine benefit obligations: July 1, 2016 December 31, 2015 Pension plans Discount rate 3.9 % 4.6 % Annual salary increase 3.5 3.7 Pension band increase (*) 2.0 2.0 Other postretirement benefit plans Discount rate 3.6 4.4 Annual salary increase 3.5 3.7 (*) Only applicable to the Nicor Gas union employees. The pension bands for the former Nicor plan have been updated to reflect the new negotiated rates for each of 2016 and 2017 of 2.0% , as indicated in the union agreement dated March 2014.
Schedule of Health Care Cost Trend Rates	The weighted average medical care cost trend rates used in measuring the APBO for the successor period ended September 30, 2016 as of the new measurement date, July 1, 2016, and for the predecessor period ended December 31, 2015 were as follows: Initial Cost Trend Rate Ultimate Cost Trend Rate Year That Ultimate Rate is Reached Successor – July 1, 2016 Pre-65 6.8 % 4.5 % 2038 Post-65 medical 8.8 4.5 2038 Post-65 prescription 8.8 4.5 2038 Predecessor – December 31, 2015 Pre-65 6.8 4.5 2038 Post-65 medical 8.8 4.5 2038 Post-65 prescription 8.8 4.5 2038
Schedule of Net Benefit Costs	Components of the net periodic benefit costs for the periods presented were as follows: Pension Plan (in millions) Successor – July 1, 2016 through September 30, 2016 Service cost (a) $ 7 Interest cost (a) 10 Expected return on plan assets (17 ) Amortization of regulatory asset 6 Net periodic pension cost $ 6 Predecessor – January 1, 2016 through June 30, 2016 Service cost (a) $ 13 Interest cost (a) 21 Expected return on plan assets (33 ) Amortization: Prior service costs (1 ) Net (gain)/loss 13 Net periodic pension cost $ 13 Predecessor – Three Months Ended September 30, 2015 Service cost $ 7 Interest cost 11 Expected return on plan assets (16 ) Amortization: Prior service costs (1 ) Net (gain)/loss 8 Net periodic pension cost $ 9 Predecessor – Nine Months Ended September 30, 2015 Service cost $ 21 Interest cost 34 Expected return on plan assets (49 ) Amortization: Prior service costs (2 ) Net (gain)/loss 23 Net periodic pension cost $ 27 (a) Effective January 1, 2016, Southern Company Gas uses a spot rate approach to estimate the service cost and interest cost components. Historically, Southern Company Gas estimated these components using a single weighted-average discount rate. Postretirement Benefits (in millions) Successor – July 1, 2016 through September 30, 2016 Service cost (a) $ 1 Interest cost (a) 2 Expected return on plan assets (2 ) Amortization of regulatory asset 1 Net periodic postretirement benefit cost $ 2 Predecessor – January 1, 2016 through June 30, 2016 Service cost (a) $ 1 Interest cost (a) 5 Expected return on plan assets (3 ) Amortization: Prior service costs (1 ) Net (gain)/loss 2 Net periodic postretirement benefit cost $ 4 Predecessor – Three Months Ended September 30, 2015 Service cost $ — Interest cost 4 Expected return on plan assets (1 ) Amortization: Prior service costs (1 ) Net (gain)/loss 1 Net periodic postretirement benefit cost $ 3 Predecessor – Nine Months Ended September 30, 2015 Service cost $ 1 Interest cost 10 Expected return on plan assets (5 ) Amortization: Prior service costs (2 ) Net (gain)/loss 4 Net periodic postretirement benefit cost $ 8 (a) Effective January 1, 2016, Southern Company Gas uses a spot rate approach to estimate the service cost and interest cost components. Historically, Southern Company Gas estimated these components using a single weighted-average discount rate.

Derivatives (Tables)

Derivatives (Tables)	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments	At September 30, 2016 , the net volume of energy-related derivative contracts for natural gas positions for Southern Company Gas, together with the longest hedge date over which it is hedging its exposure to the variability in future cash flows for forecasted transactions and the longest non-hedge date for derivatives not designated as hedges, were as follows: Successor Net Purchased/(Sold) mmBtu Longest Hedge Date Longest Non-hedge Date (in millions) 214 2018 2022
Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location	At September 30, 2016 and December 31, 2015 , the value of energy-related derivatives and interest rate derivatives was reflected in the balance sheets as follows: Asset Derivatives Liability Derivatives Successor Predecessor Successor Predecessor Derivative Category Balance Sheet Location September 30, 2016 December 31, 2015 Balance Sheet Location September 30, 2016 December 31, 2015 (in millions) (in millions) (in millions) (in millions) Derivatives designated as hedging instruments for regulatory purposes Energy-related derivatives Assets from risk management activities – current $ 8 $ 10 Liabilities from risk management activities – current $ (6 ) $ (28 ) Other deferred charges and assets — — Other deferred credits and liabilities — (2 ) Total derivatives designated as hedging instruments for regulatory purposes $ 8 $ 10 $ (6 ) $ (30 ) Derivatives designated as hedging instruments in cash flow and fair value hedges Energy-related derivatives Assets from risk management activities – current $ 2 $ 3 Liabilities from risk management activities – current $ (3 ) $ (5 ) Other deferred charges and assets — — Other deferred credits and liabilities (1 ) (2 ) Interest rate derivatives: Assets from risk management activities – current — 9 Liabilities from risk management activities – current — — Total derivatives designated as hedging instruments in cash flow and fair value hedges $ 2 $ 12 $ (4 ) $ (7 ) Derivatives not designated as hedging instruments Energy-related derivatives Assets from risk management activities – current $ 304 $ 741 Liabilities from risk management activities – current $ (345 ) $ (644 ) Other deferred charges and assets 58 179 Other deferred credits and liabilities (74 ) (185 ) Total derivatives not designated as hedging instruments $ 362 $ 920 $ (419 ) $ (829 ) Gross amount of recognized assets and liabilities (a) (b) $ 372 $ 942 $ (429 ) $ (866 ) Gross amounts offset in the balance sheet (b) (258 ) (724 ) 369 820 Net amounts of derivatives assets and liabilities, presented in the balance sheet (c) $ 114 $ 218 $ (60 ) $ (46 )
Pre Tax Effect of Unrealized Derivative Gains (Losses)	At September 30, 2016 and December 31, 2015 , the pre-tax effects of unrealized derivative gains (losses) arising from energy-related derivative instruments designated as regulatory hedging instruments and deferred were as follows: Unrealized Losses Unrealized Gains Successor Predecessor Successor Predecessor Derivative Category Balance Sheet Location September 30, 2016 December 31, 2015 Balance Sheet Location September 30, 2016 December 31, 2015 (in millions) (in millions) (in millions) (in millions) Energy-related derivatives: Other regulatory assets, current $ (3 ) $ (15 ) Other regulatory liabilities, current $ 3 $ 15 Other regulatory assets, deferred — (2 ) Other regulatory liabilities, deferred — — Total energy-related derivative gains (losses) $ (3 ) $ (17 ) $ 3 $ 15
Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss)	For the successor period July 1, 2016 through September 30, 2016 and the predecessor period three months ended September 30, 2015 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments recognized in OCI and those reclassified from accumulated OCI into earnings were as follows: Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Successor Predecessor Successor Predecessor Derivatives in Cash Flow Hedging Relationships July 1, 2016 through September 30, 2016 Three Months Ended September 30, 2015 Statements of Income Location July 1, 2016 through September 30, 2016 Three Months Ended September 30, 2015 (in millions) (in millions) (in millions) (in millions) Energy-related derivatives $ — $ (2 ) Cost of natural gas $ — $ (2 ) Interest rate derivatives (5 ) (46 ) Interest expense, net of amounts capitalized — 1 Total derivatives in cash flow hedging relationships $ (5 ) $ (48 ) $ — $ (1 ) For the predecessor periods January 1, 2016 through June 30, 2016 and nine months ended September 30, 2015 , the pre-tax effects of energy-related derivatives and interest rate derivatives designated as cash flow hedging instruments recognized in OCI and those reclassified from accumulated OCI into earnings were as follows: Gain (Loss) Recognized in OCI on Derivative (Effective Portion) Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Predecessor Predecessor Derivatives in Cash Flow Hedging Relationships January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 Statements of Income Location January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 (in millions) (in millions) Energy-related derivatives $ — $ (3 ) Cost of natural gas $ (1 ) $ (6 ) Other operations and maintenance — (1 ) Interest rate derivatives (64 ) (1 ) Interest expense, net of amounts capitalized — 2 Total derivatives in cash flow hedging relationships $ (64 ) $ (4 ) $ (1 ) $ (5 )
Pre Tax Effect of Interest Rate and Foreign Currency Derivatives	For the successor period July 1, 2016 through September 30, 2016 and the predecessor periods January 1, 2016 through June 30, 2016 and three and nine months ended September 30, 2015 , the pre-tax effects of energy-related derivatives and interest rate derivatives not designated as hedging instruments were as follows: Derivatives in Non-Designated Hedging Relationships Gain (Loss) Successor Predecessor Derivative Category Statements of Income Location July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 Three Months Ended September 30, 2015 Nine Months Ended September 30, 2015 (millions) (millions) Energy-related derivatives Natural gas revenues (*) $ — $ (1 ) $ 29 $ 7 Cost of natural gas 6 (62 ) 1 3 Total derivatives in non-designated hedging relationships $ 6 $ (63 ) $ 30 $ 10 (*) Excludes gains (losses) recorded in natural gas revenues associated with weather derivatives of $3 million for the predecessor period January 1, 2016 through June 30, 2016 and of $(1) million for the predecessor nine months ended September 30, 2015. There were no amounts recorded for the successor period July 1, 2016 through September 30, 2016 and the predecessor three months ended September 30, 2015.

Merger and Acquisition (Tables)

Merger and Acquisition (Tables)	9 Months Ended
	Sep. 30, 2016
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The following table presents the preliminary purchase price allocation: Successor Predecessor New Basis Old Basis Change in Basis (in millions) (in millions) Current assets $ 1,557 $ 1,474 $ 83 Property, plant, and equipment 10,108 10,148 (40 ) Goodwill 5,937 1,813 4,124 Other intangible assets 400 101 299 Regulatory assets 1,118 679 439 Other assets 229 273 (44 ) Current liabilities (2,201 ) (2,205 ) 4 Other liabilities (4,712 ) (4,600 ) (112 ) Long-term debt (4,261 ) (3,709 ) (552 ) Contingently redeemable noncontrolling interest (174 ) (41 ) (133 ) Total purchase price/equity $ 8,001 $ 3,933 $ 4,068

Segment and Related Information

Segment and Related Information (Tables)	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Business segment financial data for the successor period July 1, 2016 through September 30, 2016 and the predecessor periods January 1, 2016 through June 30, 2016 and three and nine months ended September 30, 2015 was as follows: Gas distribution operations Gas marketing services Wholesale gas services (*) Gas midstream operations All other Intercompany eliminations Consolidated (in millions) Successor – July 1, 2016 through September 30, 2016 Operating revenues $ 455 $ 126 $ (8 ) $ 13 $ 2 $ (45 ) $ 543 EBIT 75 (6 ) (17 ) 25 (27 ) — 50 Segment net income (loss) 27 (4 ) (11 ) 14 (22 ) — 4 Capital expenditures 268 3 1 19 7 — 298 Successor – Total assets at September 30, 2016 $ 16,184 $ 1,991 $ 1,007 $ 2,165 $ 10,274 $ (10,436 ) $ 21,185 (in millions) Predecessor – January 1, 2016 through June 30, 2016 Operating revenues $ 1,575 $ 435 $ (32 ) $ 25 $ 4 $ (102 ) $ 1,905 EBIT 353 109 (68 ) (6 ) (60 ) — 328 Segment net income (loss) 178 58 (42 ) (4 ) (59 ) — 131 Capital expenditures 484 4 1 43 16 — 548 Predecessor – Three Months Ended September 30, 2015 Operating revenues $ 445 $ 134 $ 34 $ 12 $ — $ (41 ) $ 584 EBIT 86 11 18 (16 ) (37 ) — 62 Segment net income (loss) 34 9 11 (9 ) (34 ) — 11 Capital expenditures 273 2 1 8 9 — 293 Predecessor – Nine Months Ended September 30, 2015 Operating revenues $ 2,332 $ 628 $ 128 $ 42 $ 9 $ (160 ) $ 2,979 EBIT 420 115 66 (20 ) (41 ) — 540 Segment net income (loss) 202 65 40 (12 ) (49 ) — 246 Capital expenditures 691 6 2 18 28 — 745 Predecessor – Total assets at December 31, 2015 $ 12,517 $ 686 $ 935 $ 692 $ 9,664 $ (9,740 ) $ 14,754 (*) The revenues for wholesale gas services are netted with costs associated with its energy and risk management activities. A reconciliation of operating revenues and intercompany revenues is shown in the following table. Wholesale gas services Third party gross revenues Intercompany revenues Total gross Less gross Operating (in millions) Successor – July 1, 2016 through September 30, 2016 $ 1,688 77 1,765 1,773 $ (8 ) Predecessor – (in millions) January 1, 2016 through June 30, 2016 $ 2,500 143 2,643 2,675 $ (32 ) Three months ended September 30, 2015 $ 1,440 90 1,530 1,496 $ 34 Nine months ended September 30, 2015 $ 4,876 329 5,205 5,077 $ 128
Reconciliation of Revenue from Segments to Consolidated	A reconciliation of operating revenues and intercompany revenues is shown in the following table. Wholesale gas services Third party gross revenues Intercompany revenues Total gross Less gross Operating (in millions) Successor – July 1, 2016 through September 30, 2016 $ 1,688 77 1,765 1,773 $ (8 ) Predecessor – (in millions) January 1, 2016 through June 30, 2016 $ 2,500 143 2,643 2,675 $ (32 ) Three months ended September 30, 2015 $ 1,440 90 1,530 1,496 $ 34 Nine months ended September 30, 2015 $ 4,876 329 5,205 5,077 $ 128

Non-Wholly Owned Entities and31

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2016
Equity Method Investments and Joint Ventures [Abstract]
Temporary Equity	The roll-forwards of the redeemable noncontrolling interest for the successor period July 1, 2016 through September 30, 2016 and the predecessor period January 1, 2016 through June 30, 2016 are detailed below: Predecessor – (in millions) Balance at December 31, 2015 $ — Reclassification of noncontrolling interest to contingently redeemable noncontrolling interest 46 Net income attributable to noncontrolling interest 14 Distribution to noncontrolling interest (19 ) Balance at June 30, 2016 $ 41 Successor – (in millions) Balance at July 1, 2016 $ 174 Reclassification of noncontrolling interest to mandatorily redeemable noncontrolling interest (174 ) Balance at September 30, 2016 $ —
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net	The SouthStar amounts exclude intercompany eliminations and the balances of Southern Company Gas' wholly-owned, direct subsidiary with an 85% ownership interest in SouthStar. September 30, 2016 December 31, 2015 Successor Predecessor Consolidated SouthStar % Consolidated SouthStar % (in millions) (in millions) Current assets $ 1,759 $ 210 12 % $ 2,115 $ 245 12 % Goodwill and other intangible assets 6,317 110 2 1,922 114 6 Deferred charges and other assets 13,109 17 — 10,717 16 — Total Assets $ 21,185 $ 337 2 % $ 14,754 $ 375 3 % Current liabilities $ 2,321 $ 46 2 % $ 2,918 $ 54 2 % Deferred credits and other liabilities 9,829 1 — 7,861 — — Total Liabilities 12,150 47 — 10,779 54 1 Total Stockholders' Equity 9,035 290 3 3,975 321 8 Total Liabilities and Stockholders' Equity $ 21,185 $ 337 2 % $ 14,754 $ 375 3 %
Schedule of Variable Interest Entities	The following table provides information on SouthStar’s operating revenues and operating expenses for the periods presented, which are consolidated within Southern Company Gas' statements of income. Successor Predecessor Successor Predecessor Three Months Ended September 30, 2016 Three Months Ended September 30, 2015 July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 (in millions) (in millions) (in millions) (in millions) Total operating revenues $ 100 $ 103 $ 100 $ 372 $ 536 Operating Expenses: Cost of natural gas 77 78 77 234 370 Other operations and maintenance 18 18 18 40 59 Depreciation and amortization 3 2 3 4 7 Taxes other than income taxes — — — 1 1 Total operating expenses 98 98 98 279 437 Operating Income $ 2 $ 5 $ 2 $ 93 $ 99
Equity Method Investments	Accordingly, summarized income statement information for SNG is presented below. Successor SNG September 1, 2016 through September 30, 2016 (in millions) Revenues $ 82 Operating income 60 Net income $ 55 Balance Sheet Information The carrying amounts within Southern Company Gas' balance sheets of its investments that are accounted for using the equity method were as follows: Successor Predecessor September 30, 2016 December 31, 2015 (in millions) (in millions) SNG $ 1,414 $ — Triton 45 49 Horizon Pipeline 31 14 Atlantic Coast Pipeline 23 7 PennEast Pipeline 17 9 Other 1 1 Total $ 1,531 $ 80
Schedule of Other Nonoperating Income, by Component	Income Statement Information The following table provides the income from equity method investments as recorded on Southern Company Gas' statements of income for the periods presented. Successor Predecessor Successor Predecessor Three Months Ended September 30, 2016 Three Months Ended September 30, 2015 July 1, 2016 through September 30, 2016 January 1, 2016 through June 30, 2016 Nine Months Ended September 30, 2015 (in millions) (in millions) (in millions) (in millions) SNG $ 27 $ — $ 27 $ — $ — Triton 1 2 1 1 3 Atlantic Coast Pipeline 1 — 1 — — Horizon Pipeline — — — 1 1 Total $ 29 $ 2 $ 29 $ 2 $ 4

Introduction - Narrative (Detai

Introduction - Narrative (Details) - New Accounting Pronouncement, Early Adoption, Effect [Member] - Accounting Standards Update 2015-17 [Member] $ in Millions	Dec. 31, 2015USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from deferred income taxes, current	$ 31
Reclassification to non-current accumulated deferred income taxes	$ 31

Introduction - Goodwill and Oth

Introduction - Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Successor [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Gross Carrying Amount	$ 400
Accumulated Amortization	(20)
Other Intangible Assets, Net	380
Goodwill	5,937
Amortization of intangible assets	20
Successor [Member] | Gas Distribution Operations [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Goodwill	4,672
Successor [Member] | Gas Marketing Services [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Goodwill	1,265
Successor [Member] | Gas Marketing Services [Member] | Customer Relationships [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Gross Carrying Amount	221
Accumulated Amortization	(15)
Other Intangible Assets, Net	206
Successor [Member] | Gas Marketing Services [Member] | Trade Names [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Gross Carrying Amount	115
Accumulated Amortization	(1)
Other Intangible Assets, Net	114
Successor [Member] | Wholesale Gas Services [Member] | Storage and Transportation Contracts [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Gross Carrying Amount	64
Accumulated Amortization	(4)
Other Intangible Assets, Net	$ 60
Predecessor [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Accumulated Amortization			$ (68)
Goodwill			1,813
Amortization of intangible assets		$ 8
Predecessor [Member] | Gas Marketing Services [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Other Intangible Assets, Net			$ 109
Minimum [Member] | Successor [Member] | Gas Marketing Services [Member] | Customer Relationships [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Estimated Useful Life	11 years
Minimum [Member] | Successor [Member] | Gas Marketing Services [Member] | Trade Names [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Estimated Useful Life	10 years
Minimum [Member] | Successor [Member] | Wholesale Gas Services [Member] | Storage and Transportation Contracts [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Estimated Useful Life	1 year
Maximum [Member] | Successor [Member] | Gas Marketing Services [Member] | Customer Relationships [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Estimated Useful Life	14 years
Maximum [Member] | Successor [Member] | Gas Marketing Services [Member] | Trade Names [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Estimated Useful Life	28 years
Maximum [Member] | Successor [Member] | Wholesale Gas Services [Member] | Storage and Transportation Contracts [Member]
Schedule of Intangible Assets and Goodwill [Line Items]
Estimated Useful Life	5 years

Introduction - Expected Amortiz

Introduction - Expected Amortization Expense (Details) - Successor [Member] $ in Millions	Sep. 30, 2016USD ($)
Finite-Lived Intangible Assets [Line Items]
2,017	$ 73
2,018	58
2,019	40
2,020	28
2,021	$ 21

Contingencies and Regulatory 35

Contingencies and Regulatory Matters - Narrative (Details) $ in Millions	Sep. 01, 2016USD ($)	Aug. 01, 2016USD ($)	Mar. 09, 2016USD ($)mi	Oct. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2014USD ($)	Feb. 28, 2015USD ($)
Elizabethtown Gas [Member]
Regulated Operations [Line Items]
Rate credits provided to customer, amount						$ 18
Illinois Commission [Member]
Regulated Operations [Line Items]
Loss contingency, damages sought							$ 18
CUB [Member]
Regulated Operations [Line Items]
Loss contingency, damages sought							$ 22
True-up Recovery [Member] | Atlanta Gas Light [Member]
Regulated Operations [Line Items]
Allowable amount of costs incurred to be recovered				$ 144
Unrecovered program revenue to be recovered								$ 178
Integrated System Reinforcement Program [Member] | Atlanta Gas Light [Member]
Regulated Operations [Line Items]
Program duration period		4 years
Additional investment over next four years, petitioned amount		$ 177
SAVE Program [Member] | Virginia Natural Gas [Member]
Regulated Operations [Line Items]
Natural gas pipeline, approved for replacement, more than (in miles) | mi			200
Approved infrastructure replacement program amount, remainder of year			$ 30
Approved infrastructure replacement program amount, 2017			35
Approved infrastructure replacement program amount, 2018			35
Approved infrastructure replacement program amount, 2019			35
Approved infrastructure replacement program amount, 2020			35
Approved infrastructure replacement program amount, 2021			$ 35
Aging Infrastructure Replacement Program [Member] | Elizabethtown Gas [Member]
Regulated Operations [Line Items]
Additional revenue requirement requested	$ 19
Return on equity (as a percent)	10.25%
Unfavorable Regulatory Action [Member] | Nicor Gas [Member]
Regulated Operations [Line Items]
Loss contingency, damages sought					$ 0.3
Successor [Member]
Regulated Operations [Line Items]
Amount recorded						433
Accrued environmental remediation liabilities, current						59
Successor [Member] | Elizabethtown Gas [Member]
Regulated Operations [Line Items]
Rate credits provided to customer, amount						18
North Carolina Environmental [Member] | Successor [Member]
Regulated Operations [Line Items]
Amount recorded						$ 5

Contingencies and Regulatory 36

Contingencies and Regulatory Matters - Estimated Recognition of Rate Making Assets (Details) - Regulatory Asset Off Balance Sheet [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Predecessor [Member]
Regulatory Assets [Line Items]
Regulatory Asset		$ 122
Predecessor [Member] | Atlanta Gas Light [Member]
Regulatory Assets [Line Items]
Regulatory Asset		103
Predecessor [Member] | Virginia Natural Gas [Member]
Regulatory Assets [Line Items]
Regulatory Asset		12
Predecessor [Member] | Elizabethtown Gas [Member]
Regulatory Assets [Line Items]
Regulatory Asset		4
Predecessor [Member] | Nicor Gas [Member]
Regulatory Assets [Line Items]
Regulatory Asset		$ 3
Successor [Member]
Regulatory Assets [Line Items]
Regulatory Asset	$ 130
Successor [Member] | Atlanta Gas Light [Member]
Regulatory Assets [Line Items]
Regulatory Asset	109
Successor [Member] | Virginia Natural Gas [Member]
Regulatory Assets [Line Items]
Regulatory Asset	12
Successor [Member] | Elizabethtown Gas [Member]
Regulatory Assets [Line Items]
Regulatory Asset	6
Successor [Member] | Nicor Gas [Member]
Regulatory Assets [Line Items]
Regulatory Asset	$ 3

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Sep. 30, 2016USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral held on deposit in broker margin accounts	$ 111
Successor [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Weather derivative premium	7
Collateral held on deposit in broker margin accounts	$ 111

Fair Value Measurements - Deriv

Fair Value Measurements - Derivative Assets and Liabilities (Details) - Successor [Member] $ in Millions	Sep. 30, 2016USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy-related derivatives	$ 372
Net Asset Value as a Practical Expedient (NAV)	0
Energy-related derivatives	429
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy-related derivatives	365
Total	365
Energy-related derivatives	429
Total	429
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy-related derivatives	203
Total	203
Energy-related derivatives	267
Total	267
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy-related derivatives	162
Total	162
Energy-related derivatives	162
Total	162
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Energy-related derivatives	0
Total	0
Energy-related derivatives	0
Total	$ 0

Fair Value Measurements - Amort

Fair Value Measurements - Amortized Cost and Fair Value of Long-Term Debt (Details) - Successor [Member] - Significant other observable inputs (Level 2) [Member] $ in Millions	Sep. 30, 2016USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including securities due within one year carrying amount	$ 5,414
Long-term debt, including securities due within one year fair value	$ 5,383

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in treasury shares)			200,000
Beginning Balance	$ 3,933		$ 3,975	$ 3,828
Consolidated Net Income Attributable to Southern Company Gas		$ 11	131	246
Other comprehensive income (loss)			(35)	11
Stock issued			6	9
Stock-based compensation			30	2
Cash dividends on common stock			(128)	(183)
Distribution to noncontrolling interest				(18)
Reclassification of noncontrolling interest			(46)
Net income attributable to noncontrolling interest		1	14	15
Ending Balance		$ 3,910	$ 3,933	$ 3,910
Predecessor [Member] | Common Shares Issued [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in shares)	120,742,000		120,377,000	119,647,000
Stock issued (in shares)			95,000	173,000
Stock-based compensation (in shares)			270,000	429,000
Ending Balance (in shares)		120,249,000	120,742,000	120,249,000
Predecessor [Member] | Common Shares Treasury [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in treasury shares)	217,000		217,000	217,000
Ending Balance (in treasury shares)		217,000	217,000	217,000
Predecessor [Member] | Common Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 3,933		$ 3,929	$ 3,784
Consolidated Net Income Attributable to Southern Company Gas			131	246
Other comprehensive income (loss)			(35)	11
Stock issued			6	9
Stock-based compensation			30	2
Cash dividends on common stock			(128)	(183)
Ending Balance		$ 3,869	3,933	3,869
Predecessor [Member] | Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	0		46	44
Distribution to noncontrolling interest				(18)
Reclassification of noncontrolling interest			(46)
Net income attributable to noncontrolling interest				15
Ending Balance		$ 41	0	$ 41
Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	8,001
Consolidated Net Income Attributable to Southern Company Gas	4
Capital contributions from parent company	1,089
Other comprehensive income (loss)	(3)
Stock-based compensation	7
Cash dividends on common stock	(63)
Net income attributable to noncontrolling interest	$ 0
Ending Balance (in treasury shares)	0
Ending Balance	$ 9,035		$ 8,001
Successor [Member] | Common Shares Issued [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in shares)	0
Ending Balance (in shares)	0		0
Successor [Member] | Common Shares Treasury [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in treasury shares)	0
Ending Balance (in treasury shares)	0		0
Successor [Member] | Common Stockholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 8,001
Consolidated Net Income Attributable to Southern Company Gas	4
Capital contributions from parent company	1,089
Other comprehensive income (loss)	(3)
Stock-based compensation	7
Cash dividends on common stock	(63)
Ending Balance	9,035		$ 8,001
Successor [Member] | Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	0
Ending Balance	$ 0		$ 0

Financing - Bank Credit Arrange

Financing - Bank Credit Arrangements (Details) $ in Millions	Sep. 30, 2016USD ($)
Line of Credit Facility [Line Items]
Expires 2,017	$ 75
Expires 2,018	1,925
Total	2,000
Unused	1,947
Southern Company Gas Capital [Member]
Line of Credit Facility [Line Items]
Expires 2,017	49
Expires 2,018	1,251
Total	1,300
Unused	1,247
Nicor Gas [Member]
Line of Credit Facility [Line Items]
Expires 2,017	26
Expires 2,018	674
Total	700
Unused	$ 700

Financing (Details)

Financing (Details)	Oct. 27, 2016USD ($)	Jul. 31, 2016USD ($)	May 31, 2016USD ($)	Feb. 29, 2016USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2016USD ($)series	Sep. 01, 2016	Jun. 30, 2016USD ($)
Gas Facility Revenue Bonds [Member]
Debt Instrument [Line Items]
Number of series issued | series						5
Outstanding					$ 200,000,000	$ 200,000,000
Senior Notes [Member] | Southern Company Gas Capital [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount			$ 350,000,000
Stated interest rate (as a percent)		6.375%	3.25%
Repayments of senior notes		$ 300,000,000
Callable Debt [Member]
Debt Instrument [Line Items]
Outstanding					155,000,000	155,000,000
Current portion of long-term debt					120,000,000	120,000,000		$ 275,000,000
First Mortgage Bonds [Member] | Secured Debt [Member] | Nicor Gas [Member]
Debt Instrument [Line Items]
Repayments of first mortgage bond			$ 50,000,000	$ 75,000,000
Issuance of debt, principal amount								250,000,000
First Mortgage Bonds Due 2026 [Member] | Secured Debt [Member] | Nicor Gas [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount								$ 100,000,000
Stated interest rate (as a percent)								2.66%
First Mortgage Bonds Due 2031 [Member] | Secured Debt [Member] | Nicor Gas [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount								$ 100,000,000
Stated interest rate (as a percent)								2.91%
First Mortgage Bonds Due 2036 [Member] | Secured Debt [Member] | Nicor Gas [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount								$ 50,000,000
Stated interest rate (as a percent)								3.27%
Senior Notes due October 1, 2023 [Member] | Senior Notes [Member] | Southern Company Gas Capital [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount					$ 350,000,000	$ 350,000,000
Stated interest rate (as a percent)					2.45%	2.45%
Senior Notes Due October 2046 [Member] | Senior Notes [Member] | Southern Company Gas Capital [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount					$ 550,000,000	$ 550,000,000
Stated interest rate (as a percent)					3.95%	3.95%
Senior Promissory Note [Member] | Senior Notes [Member] | Southern Company Gas Capital [Member]
Debt Instrument [Line Items]
Issuance of debt, principal amount					$ 360,000,000	$ 360,000,000
Subsequent Event [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Repayments of senior notes	$ 120,000,000
Successor [Member]
Debt Instrument [Line Items]
Repayments of first mortgage bond					0
Repayments of senior notes					$ 300,000,000
Successor [Member] | SNG [Member]
Debt Instrument [Line Items]
Equity interest (as a percent)					50.00%	50.00%	50.00%

Retirement Benefits - Actuarial

Retirement Benefits - Actuarial Assumptions (Details)	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Jul. 01, 2016
Successor [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate – interest costs, Assumptions used to determine net period costs (as a percent)	3.20%
Discount rate – service costs, Assumptions used to determine net period costs (as a percent)	4.10%
Expected long-term return on plan assets, Assumptions used to determine net period costs (as a percent)	7.80%
Annual salary increase, Assumptions used to determine net period costs (as a percent)	3.50%
Pension band increase, Assumptions used to determine net period costs (as a percent)	2.00%
Discount rate, Assumptions used to determine benefit obligations (as a percent)					3.90%
Annual salary increase, Assumptions used to determine benefit obligations (as a percent)					3.50%
Pension band increase, Assumptions used to determine benefit obligations (as a percent)	2.00%
Successor [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate – interest costs, Assumptions used to determine net period costs (as a percent)	2.80%
Discount rate – service costs, Assumptions used to determine net period costs (as a percent)	4.00%
Expected long-term return on plan assets, Assumptions used to determine net period costs (as a percent)	6.10%
Annual salary increase, Assumptions used to determine net period costs (as a percent)	3.50%
Discount rate, Assumptions used to determine benefit obligations (as a percent)					3.60%
Annual salary increase, Assumptions used to determine benefit obligations (as a percent)					3.50%
Predecessor [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate – interest costs, Assumptions used to determine net period costs (as a percent)		4.00%	4.20%
Discount rate – service costs, Assumptions used to determine net period costs (as a percent)		4.80%	4.20%
Expected long-term return on plan assets, Assumptions used to determine net period costs (as a percent)		7.80%	7.80%
Annual salary increase, Assumptions used to determine net period costs (as a percent)		3.70%	3.70%
Pension band increase, Assumptions used to determine net period costs (as a percent)		2.00%	2.00%
Discount rate, Assumptions used to determine benefit obligations (as a percent)				4.60%
Annual salary increase, Assumptions used to determine benefit obligations (as a percent)				3.70%
Pension band increase, Assumptions used to determine benefit obligations (as a percent)				2.00%
Predecessor [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate – interest costs, Assumptions used to determine net period costs (as a percent)		3.60%	4.00%
Discount rate – service costs, Assumptions used to determine net period costs (as a percent)		4.70%	4.00%
Expected long-term return on plan assets, Assumptions used to determine net period costs (as a percent)		6.60%	7.40%
Annual salary increase, Assumptions used to determine net period costs (as a percent)		3.70%	3.70%
Discount rate, Assumptions used to determine benefit obligations (as a percent)				4.40%
Annual salary increase, Assumptions used to determine benefit obligations (as a percent)				3.70%

Retirement Benefits - Health Ca

Retirement Benefits - Health Care Cost Trend Rates (Details)	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Jul. 01, 2016
Successor [Member] | Pre-65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate (as a percent)	6.80%
Ultimate Cost Trend Rate (as a percent)	4.50%
Year That Ultimate Rate is Reached			2,038
Successor [Member] | Post-65 Medical [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate (as a percent)	8.80%
Ultimate Cost Trend Rate (as a percent)	4.50%
Year That Ultimate Rate is Reached			2,038
Successor [Member] | Post-65 Prescription [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate (as a percent)	8.80%
Ultimate Cost Trend Rate (as a percent)	4.50%
Year That Ultimate Rate is Reached			2,038
Predecessor [Member] | Pre-65 [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate (as a percent)		6.80%
Ultimate Cost Trend Rate (as a percent)		4.50%
Year That Ultimate Rate is Reached		2,038
Predecessor [Member] | Post-65 Medical [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate (as a percent)		8.80%
Ultimate Cost Trend Rate (as a percent)		4.50%
Year That Ultimate Rate is Reached		2,038
Predecessor [Member] | Post-65 Prescription [Member]
Defined Benefit Plan Disclosure [Line Items]
Initial Cost Trend Rate (as a percent)		8.80%
Ultimate Cost Trend Rate (as a percent)		4.50%
Year That Ultimate Rate is Reached		2,038

Retirement Benefits - Component

Retirement Benefits - Components of Pension and Other Retirement Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7
Interest cost	10
Expected return on plan assets	(17)
Amortization of regulatory asset	6
Amortization:
Net periodic benefit cost	6
Successor [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1
Interest cost	2
Expected return on plan assets	(2)
Amortization of regulatory asset	1
Amortization:
Net periodic benefit cost	$ 2
Predecessor [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 7	$ 13	$ 21
Interest cost		11	21	34
Expected return on plan assets		(16)	(33)	(49)
Amortization:
Prior service costs		(1)	(1)	(2)
Net (gain)/loss		8	13	23
Net periodic benefit cost		9	13	27
Predecessor [Member] | Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	1	1
Interest cost		4	5	10
Expected return on plan assets		(1)	(3)	(5)
Amortization:
Prior service costs		(1)	(1)	(2)
Net (gain)/loss		1	2	4
Net periodic benefit cost		$ 3	$ 4	$ 8

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discretionary contributions made to qualified plan	$ 125,000,000
Mandatory contributions expected to be made during fiscal year			$ 0
Increase (decrease) projected benefit obligations		$ 177,000,000
Increase (decrease) in plan assets		(10,000,000)
Welfare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) projected benefit obligations		20,000,000
Increase (decrease) in plan assets		$ 1,000,000
Successor [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension band increase, Assumptions used to determine benefit obligations (as a percent)		2.00%
Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension band increase, Assumptions used to determine benefit obligations (as a percent)				2.00%	2.00%
Pension and Other Postretirement Plans Costs [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory asset	$ 437,000,000	$ 437,000,000	$ 437,000,000

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details)	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Income Taxes [Line Items]
Effective income tax rate (as a percent)	59.60%
Effective income tax rate, excluding merger related impact (as a percent)	39.10%
Predecessor [Member]
Income Taxes [Line Items]
Effective income tax rate (as a percent)		37.60%	37.90%
Effective income tax rate, excluding merger related impact (as a percent)		37.50%

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) MMBTU in Billions	Jan. 23, 2015USD ($)	Sep. 30, 2016USD ($)	May 31, 2016USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2016USD ($)	Sep. 30, 2016USD ($)MMBTU	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)	Nov. 30, 2015USD ($)
Derivative [Line Items]
Collateral held on deposit in broker margin accounts		$ 111,000,000		$ 111,000,000			$ 111,000,000
Long [Member]
Derivative [Line Items]
Net notional amount (in btu) | MMBTU							3.2
Short [Member]
Derivative [Line Items]
Net notional amount (in btu) | MMBTU							2.9
Successor [Member]
Derivative [Line Items]
Collateral held on deposit in broker margin accounts		111,000,000		111,000,000			$ 111,000,000
Successor [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)				(5,000,000)
Predecessor [Member]
Derivative [Line Items]
Collateral held on deposit in broker margin accounts									$ 96,000,000
Predecessor [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)					$ (48,000,000)	$ (64,000,000)		$ (4,000,000)
Weather Derivatives [Member] | Successor [Member]
Derivative [Line Items]
Gain (loss) on derivative, net				0
Weather Derivatives [Member] | Predecessor [Member]
Derivative [Line Items]
Gain (loss) on derivative, net					0	3,000,000		(1,000,000)
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount	$ 800,000,000
Derivatives settled during period, notional amount		200,000,000	$ 400,000,000	200,000,000			$ 200,000,000			$ 200,000,000
Loss on settlement of derivative		$ 35,000,000	$ 26,000,000
Interest Rate Swap [Member] | Minimum [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative term	10 years
Interest Rate Swap [Member] | Maximum [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative term	30 years
Interest Rate Derivatives [Member] | Successor [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)				$ (5,000,000)
Interest Rate Derivatives [Member] | Predecessor [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)					$ (46,000,000)	$ (64,000,000)		$ (1,000,000)

Derivatives - Energy-related De

Derivatives - Energy-related Derivative Contracts (Details) - Successor [Member] - Gas [Member] MMBTU in Millions	9 Months Ended
	Sep. 30, 2016MMBTU
Energy Related Derivative Contracts
Net Purchased/(Sold) (in Btu)	214
Longest Hedge Date	2,018
Longest Non-hedge Date	2,022

Derivatives - Derivative Instru

Derivatives - Derivative Instruments on the Condensed Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Successor [Member]
Asset Derivatives
Asset Derivatives	$ 372
Gross amounts offset in our unaudited Condensed Consolidated Balance Sheets	(258)
Net amounts of assets presented in our unaudited Condensed Consolidated Balance Sheets	114
Liability Derivatives
Liability Derivatives	(429)
Gross amounts offset in our unaudited Condensed Consolidated Balance Sheets	369
Net amounts of liabilities presented in our unaudited Condensed Consolidated Balance Sheets	(60)
Successor [Member] | Not Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	362
Liability Derivatives
Liability Derivatives	(419)
Successor [Member] | Other Current Assets [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	304
Successor [Member] | Liabilities from Risk Management Activities [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	(345)
Successor [Member] | Other Noncurrent Assets [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	58
Successor [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	(74)
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	8
Liability Derivatives
Liability Derivatives	(6)
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Current Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	8
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Current Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	(6)
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Noncurrent Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	0
Successor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	2
Liability Derivatives
Liability Derivatives	(4)
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	2
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Assets [Member] | Interest Rate Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	(3)
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Liabilities [Member] | Interest Rate Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Noncurrent Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives	0
Successor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives	$ (1)
Predecessor [Member]
Asset Derivatives
Asset Derivatives		$ 942
Gross amounts offset in our unaudited Condensed Consolidated Balance Sheets		(724)
Net amounts of assets presented in our unaudited Condensed Consolidated Balance Sheets		218
Liability Derivatives
Liability Derivatives		(866)
Gross amounts offset in our unaudited Condensed Consolidated Balance Sheets		820
Net amounts of liabilities presented in our unaudited Condensed Consolidated Balance Sheets		(46)
Predecessor [Member] | Not Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		920
Liability Derivatives
Liability Derivatives		(829)
Predecessor [Member] | Other Current Assets [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		741
Predecessor [Member] | Liabilities from Risk Management Activities [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		(644)
Predecessor [Member] | Other Noncurrent Assets [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		179
Predecessor [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivatives [Member] | Not Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		(185)
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		10
Liability Derivatives
Liability Derivatives		(30)
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Current Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		10
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Current Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		(28)
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Noncurrent Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		0
Predecessor [Member] | Hedging Instruments for Regulatory Purposes [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		(2)
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		12
Liability Derivatives
Liability Derivatives		(7)
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		3
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Assets [Member] | Interest Rate Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		9
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		(5)
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Current Liabilities [Member] | Interest Rate Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		0
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Noncurrent Assets [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives
Asset Derivatives		0
Predecessor [Member] | Cash Flow and Fair Value Hedging [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivatives [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Liability Derivatives		$ (2)

Derivatives - Unrealized Gain (

Derivatives - Unrealized Gain (Loss) (Details) - Energy Related Derivatives [Member] - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Successor [Member]
Derivative [Line Items]
Unrealized Losses	$ (3)
Unrealized Gains	3
Predecessor [Member]
Derivative [Line Items]
Unrealized Losses		$ (17)
Unrealized Gains		15
Other regulatory assets current [Member] | Successor [Member]
Derivative [Line Items]
Unrealized Losses	(3)
Other regulatory assets current [Member] | Predecessor [Member]
Derivative [Line Items]
Unrealized Losses		(15)
Other regulatory liabilities current [Member] | Successor [Member]
Derivative [Line Items]
Unrealized Gains	3
Other regulatory liabilities current [Member] | Predecessor [Member]
Derivative [Line Items]
Unrealized Gains		15
Other regulatory assets deferred [Member] | Successor [Member]
Derivative [Line Items]
Unrealized Losses	0
Other regulatory assets deferred [Member] | Predecessor [Member]
Derivative [Line Items]
Unrealized Losses		(2)
Other regulatory liabilities deferred [Member] | Successor [Member]
Derivative [Line Items]
Unrealized Gains	$ 0
Other regulatory liabilities deferred [Member] | Predecessor [Member]
Derivative [Line Items]
Unrealized Gains		$ 0

Derivatives - Derivative Inst52

Derivatives - Derivative Instruments on the Consolidated Statements of Income (Details) - USD ($)	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	$ (5,000,000)
Net gain (loss) reclassified from OCI	0
Successor [Member] | Not Designated as Hedging Instrument [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivatives not designated as hedges	6,000,000
Predecessor [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		$ (48,000,000)	$ (64,000,000)	$ (4,000,000)
Net gain (loss) reclassified from OCI		(1,000,000)	(1,000,000)	(5,000,000)
Predecessor [Member] | Not Designated as Hedging Instrument [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivatives not designated as hedges		30,000,000	(63,000,000)	10,000,000
Weather Derivatives [Member] | Successor [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivative, net	0
Weather Derivatives [Member] | Predecessor [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivative, net		0	3,000,000	(1,000,000)
Energy Related Derivatives [Member] | Successor [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	0
Energy Related Derivatives [Member] | Successor [Member] | Natural Gas Revenue [Member] | Not Designated as Hedging Instrument [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivatives not designated as hedges	0
Energy Related Derivatives [Member] | Successor [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Net gain (loss) reclassified from OCI	0
Energy Related Derivatives [Member] | Successor [Member] | Cost of Sales [Member] | Not Designated as Hedging Instrument [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivatives not designated as hedges	6,000,000
Energy Related Derivatives [Member] | Predecessor [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		(2,000,000)	0	(3,000,000)
Energy Related Derivatives [Member] | Predecessor [Member] | Natural Gas Revenue [Member] | Not Designated as Hedging Instrument [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivatives not designated as hedges		29,000,000	(1,000,000)	7,000,000
Energy Related Derivatives [Member] | Predecessor [Member] | Cost of Sales [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Net gain (loss) reclassified from OCI		(2,000,000)	(1,000,000)	(6,000,000)
Energy Related Derivatives [Member] | Predecessor [Member] | Cost of Sales [Member] | Not Designated as Hedging Instrument [Member]
Derivatives in Non-Designated Hedging Relationships
Gain (loss) on derivatives not designated as hedges		1,000,000	(62,000,000)	3,000,000
Energy Related Derivatives [Member] | Predecessor [Member] | Operating Expense [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Net gain (loss) reclassified from OCI			0	(1,000,000)
Interest Rate Derivatives [Member] | Successor [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)	(5,000,000)
Interest Rate Derivatives [Member] | Successor [Member] | Interest Expense, net of Amounts Capitalized [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Net gain (loss) reclassified from OCI	$ 0
Interest Rate Derivatives [Member] | Predecessor [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Gain (Loss) Recognized in OCI on Derivative (Effective Portion)		(46,000,000)	(64,000,000)	(1,000,000)
Interest Rate Derivatives [Member] | Predecessor [Member] | Interest Expense, net of Amounts Capitalized [Member] | Cash Flow Hedging [Member]
Derivatives in Cash Flow Hedging Relationships
Net gain (loss) reclassified from OCI		$ 1,000,000	$ 0	$ 2,000,000

Merger and Acquisition - Narrat

Merger and Acquisition - Narrative (Details) $ / shares in Units, $ in Millions	Sep. 01, 2016USD ($)mi	Sep. 30, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)$ / sharesshares	Sep. 30, 2015USD ($)	Jun. 30, 2016USD ($)	Sep. 30, 2016USD ($)$ / sharesshares	Sep. 30, 2015USD ($)	Jul. 01, 2016$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Southern Company [Member]
Business Acquisition [Line Items]
Common stock right to convert to cash, price per share (in dollars per share) | $ / shares								$ 66
Conversion ratio, percentage of underlying stock award units (as a percent)								125.00%
Rate credits provided to customer, amount						$ 18
Shares authorized under new bylaws | shares								110,000,000
Common stock, shares authorized | shares								100,000,000
Preferred stock, shares authorized | shares								10,000,000
Common stock, par value (in dollars per share) | $ / shares								$ 0.01
Preferred Stock Par Value | $ / shares								$ 0.01
Successor [Member]
Business Acquisition [Line Items]
Goodwill		$ 5,937	$ 5,937			$ 5,937
Merger-related expenses			$ 35
Common stock, shares authorized | shares		100,000,000	100,000,000			100,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01			$ 0.01
Capital contributions from parent company			$ 1,089
Successor [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Goodwill		$ 5,900	5,900			$ 5,900
Adjustments for pushdown accounting decrease in net income, before tax			28
Adjustments for pushdown accounting decrease in net income, net of tax			17
Adjustments for pushdown accounting, decrease in revenues			29
Adjustments for pushdown accounting, increase in amortization expense			11
Adjustments for pushdown accounting, decrease in interest expense			10
Merger-related expenses			35
Merger related costs, net of tax			24
Merger related costs, compensation related expenses			15
Successor [Member] | Merger Related Expenses [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Merger-related expenses			2
Predecessor [Member]
Business Acquisition [Line Items]
Goodwill									$ 1,813
Merger-related expenses				$ 35	$ 56		$ 35
Common stock, shares authorized | shares									750,000,000
Common stock, par value (in dollars per share) | $ / shares									$ 5
Predecessor [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Merger-related expenses				35	56		35
Merger related costs, net of tax				$ 21	41		$ 21
Merger related costs, compensation related expenses					25
Predecessor [Member] | Merger Related Expenses [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Merger-related expenses					$ 31
Elizabethtown Gas [Member]
Business Acquisition [Line Items]
Rate credits provided to customer, amount			18
Elizabethtown Gas [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Regulatory approval requirements, base rate case filing period						3 years
Elizabethtown Gas [Member] | Successor [Member]
Business Acquisition [Line Items]
Rate credits provided to customer, amount			$ 18
Elkton Gas [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Regulatory approval requirements, base rate case filing period						2 years
SNG [Member]
Business Acquisition [Line Items]
Pipeline system (in miles) | mi	7,000
Equity method investment, aggregate cost	$ 1,400
Proceeds from bridge loan from Southern Company, used to finance equity method investment	360
Equity method investment, difference between carrying amount and underlying ownership interest	$ 700
SNG [Member] | Successor [Member]
Business Acquisition [Line Items]
Ownership interest (as a percent)	50.00%	50.00%	50.00%			50.00%
SNG [Member] | Southern Company [Member]
Business Acquisition [Line Items]
Capital contributions from parent company	$ 1,050
SNG [Member] | Southern Company Gas [Member]
Business Acquisition [Line Items]
Transportation costs paid to SNG prior to equity investment		$ 4

Merger and Acquisition - Schedu

Merger and Acquisition - Schedule of Acquisitions (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Successor [Member]
Business Acquisition [Line Items]
Goodwill	$ 5,937
Successor [Member] | Southern Company Gas [Member]
Business Acquisition [Line Items]
Current assets	1,557
Property, plant, and equipment	10,108
Goodwill	5,937
Other intangible assets	400
Regulatory assets	1,118
Other assets	229
Current liabilities	(2,201)
Other liabilities	(4,712)
Long-term debt	(4,261)
Contingently redeemable noncontrolling interest	(174)
Total purchase price/equity	8,001
Change in Basis
Current assets	83
Property, plant, and equipment	(40)
Goodwill	4,124
Other intangible assets	299
Regulatory assets	439
Other assets	(44)
Current liabilities	4
Other liabilities	(112)
Long-term debt	(552)
Contingently redeemable noncontrolling interest	(133)
Total purchase price/equity	$ 4,068
Predecessor [Member]
Business Acquisition [Line Items]
Goodwill			$ 1,813
Predecessor [Member] | Southern Company Gas [Member]
Business Acquisition [Line Items]
Current assets		$ 1,474
Property, plant, and equipment		10,148
Goodwill		1,813
Other intangible assets		101
Regulatory assets		679
Other assets		273
Current liabilities		(2,205)
Other liabilities		(4,600)
Long-term debt		(3,709)
Contingently redeemable noncontrolling interest		(41)
Total purchase price/equity		$ 3,933

Segment and Related Informati55

Segment and Related Information (Details)	9 Months Ended
	Sep. 30, 2016segmentstate
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
Gas Distribution Operations [Member]
Segment Reporting Information [Line Items]
Number of states in which entity operates | state	7

Segment and Related Informati56

Segment and Related Information - Financial Data for Business Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 543
EBIT	50
Segment net income (loss)	4
Capital expenditures	298
Total assets	21,185
Successor [Member] | Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(45)
EBIT	0
Segment net income (loss)	0
Capital expenditures	0
Total assets	(10,436)
Successor [Member] | Gas Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	455
EBIT	75
Segment net income (loss)	27
Capital expenditures	268
Total assets	16,184
Successor [Member] | Gas Marketing Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	126
EBIT	(6)
Segment net income (loss)	(4)
Capital expenditures	3
Total assets	1,991
Successor [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	(8)
EBIT	(17)
Segment net income (loss)	(11)
Capital expenditures	1
Total assets	1,007
Successor [Member] | Gas Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	13
EBIT	25
Segment net income (loss)	14
Capital expenditures	19
Total assets	2,165
Successor [Member] | Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	2
EBIT	(27)
Segment net income (loss)	(22)
Capital expenditures	7
Total assets	$ 10,274
Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 584	$ 1,905	$ 2,979
EBIT		62	328	540
Segment net income (loss)		11	131	246
Capital expenditures		293	548	745
Total assets					$ 14,754
Predecessor [Member] | Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues		(41)	(102)	(160)
EBIT		0	0	0
Segment net income (loss)		0	0	0
Capital expenditures		0	0	0
Total assets					(9,740)
Predecessor [Member] | Gas Distribution Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		445	1,575	2,332
EBIT		86	353	420
Segment net income (loss)		34	178	202
Capital expenditures		273	484	691
Total assets					12,517
Predecessor [Member] | Gas Marketing Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		134	435	628
EBIT		11	109	115
Segment net income (loss)		9	58	65
Capital expenditures		2	4	6
Total assets					686
Predecessor [Member] | Wholesale Gas Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		34	(32)	128
EBIT		18	(68)	66
Segment net income (loss)		11	(42)	40
Capital expenditures		1	1	2
Total assets					935
Predecessor [Member] | Gas Midstream Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		12	25	42
EBIT		(16)	(6)	(20)
Segment net income (loss)		(9)	(4)	(12)
Capital expenditures		8	43	18
Total assets					692
Predecessor [Member] | Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	4	9
EBIT		(37)	(60)	(41)
Segment net income (loss)		(34)	(59)	(49)
Capital expenditures		$ 9	$ 16	$ 28
Total assets					$ 9,664

Segment and Related Informati57

Segment and Related Information - Operating Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues	$ 543
Successor [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues	(8)
Less gross gas costs	1,773
Successor [Member] | Third Party Gross Revenues [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues	1,688
Successor [Member] | Intercompany Revenues [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues	77
Successor [Member] | Total Gross Revenues [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues	$ 1,765
Predecessor [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues		$ 584	$ 1,905	$ 2,979
Predecessor [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues		34	(32)	128
Less gross gas costs		1,496	2,675	5,077
Predecessor [Member] | Third Party Gross Revenues [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues		1,440	2,500	4,876
Predecessor [Member] | Intercompany Revenues [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues		90	143	329
Predecessor [Member] | Total Gross Revenues [Member] | Operating Segments [Member] | Wholesale Gas Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total operating revenues		$ 1,530	$ 2,643	$ 5,205

Non-Wholly Owned Entities and58

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest - Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Predecessor [Member]
Increase (Decrease) in Redeemable Noncontrolling Interest [Roll Forward]
Balance as of Beginning of Period	$ 41		$ 0
Reclassification of noncontrolling interest to contingently redeemable noncontrolling interest			46
Net income attributable to noncontrolling interest		$ 1	14	$ 15
Distribution to noncontrolling interest			(19)	$ (18)
Balance as of End of Period			41
Successor [Member]
Increase (Decrease) in Redeemable Noncontrolling Interest [Roll Forward]
Balance as of Beginning of Period	174
Reclassification of noncontrolling interest to mandatorily redeemable noncontrolling interest	(174)
Net income attributable to noncontrolling interest	0
Distribution to noncontrolling interest	0
Balance as of End of Period	$ 0		$ 174

Non-Wholly Owned Entities and59

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Oct. 03, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 01, 2016
South Star [Member]
Schedule of Equity Method Investments [Line Items]
Expenditures for property, plant and equipment	$ 1	$ 2			$ 3
Ownership interest in variable interest entity (as a percent)				85.00%
South Star [Member] | Piedmont [Member]
Schedule of Equity Method Investments [Line Items]
Payments to Noncontrolling Interests		$ 19			$ 18
Subsequent Event [Member] | South Star [Member] | Piedmont [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest to be sold (as a percent)			15.00%
Letter of agreement for sale of ownership interest			$ 160
Income from equity method investment			$ 14
Successor [Member]
Schedule of Equity Method Investments [Line Items]
Expenditures for property, plant and equipment	287
Payments to Noncontrolling Interests	0
Income from equity method investment	$ 29
SNG [Member] | Successor [Member]
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)	50.00%			50.00%		50.00%
Income from equity method investment	$ 27

Non-Wholly Owned Entities and60

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest - SouthStar's Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Successor [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Current assets	$ 1,759
Goodwill and other intangible assets	6,317
Deferred charges and other assets	13,109
Total assets	21,185
Current liabilities	2,321
Deferred credits and other liabilities	9,829
Total Liabilities	12,150
Total Stockholders' Equity	9,035	$ 8,001
Total Liabilities and Stockholders' Equity	21,185
Successor [Member] | South Star [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Current assets	$ 210
Current assets (as a percent of consolidated)	12.00%
Goodwill and other intangible assets	$ 110
Goodwill and other intangible assets (as a percent of consolidated)	2.00%
Deferred charges and other assets	$ 17
Deferred charges and other assets (as a percent of consolidated)	0.00%
Total assets	$ 337
Total assets (as a percent of consolidated)	2.00%
Current liabilities	$ 46
Current liabilities (as a percent of consolidated)	2.00%
Deferred credits and other liabilities	$ 1
Deferred credits and other liabilities (as a percent of consolidated)	0.00%
Total Liabilities	$ 47
Total Liabilities (as a percent of consolidated)	0.00%
Total Stockholders' Equity	$ 290
Total Stockholders' Equity (as a percent of consolidated)	3.00%
Total Liabilities and Stockholders' Equity	$ 337
Total liabilities and equity (as a percent of consolidated)	2.00%
Predecessor [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Current assets			$ 2,115
Goodwill and other intangible assets			1,922
Deferred charges and other assets			10,717
Total assets			14,754
Current liabilities			2,918
Deferred credits and other liabilities			7,861
Total Liabilities			10,779
Total Stockholders' Equity		$ 3,933	3,975	$ 3,910	$ 3,828
Total Liabilities and Stockholders' Equity			14,754
Predecessor [Member] | South Star [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Current assets			$ 245
Current assets (as a percent of consolidated)			12.00%
Goodwill and other intangible assets			$ 114
Goodwill and other intangible assets (as a percent of consolidated)			6.00%
Deferred charges and other assets			$ 16
Deferred charges and other assets (as a percent of consolidated)			0.00%
Total assets			$ 375
Total assets (as a percent of consolidated)			3.00%
Current liabilities			$ 54
Current liabilities (as a percent of consolidated)			2.00%
Deferred credits and other liabilities			$ 0
Deferred credits and other liabilities (as a percent of consolidated)			0.00%
Total Liabilities			$ 54
Total Liabilities (as a percent of consolidated)			1.00%
Total Stockholders' Equity			$ 321
Total Stockholders' Equity (as a percent of consolidated)			8.00%
Total Liabilities and Stockholders' Equity			$ 375
Total liabilities and equity (as a percent of consolidated)			3.00%

Non-Wholly Owned Entities and61

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest - SouthStar's Revenues and Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Variable Interest Entity [Line Items]
Total operating revenues	$ 543
Other operations and maintenance	216
Total operating expenses	531
Operating Income	12
Successor [Member] | South Star [Member]
Variable Interest Entity [Line Items]
Total operating revenues	100
Cost of natural gas	77
Other operations and maintenance	18
Depreciation and amortization	3
Taxes other than income taxes	0
Total operating expenses	98
Operating Income	$ 2
Predecessor [Member]
Variable Interest Entity [Line Items]
Total operating revenues		$ 584	$ 1,905	$ 2,979
Other operations and maintenance		218	454	676
Total operating expenses		525	1,584	2,449
Operating Income		59	321	530
Predecessor [Member] | South Star [Member]
Variable Interest Entity [Line Items]
Total operating revenues		103	372	536
Cost of natural gas		78	234	370
Other operations and maintenance		18	40	59
Depreciation and amortization		2	4	7
Taxes other than income taxes		0	1	1
Total operating expenses		98	279	437
Operating Income		$ 5	$ 93	$ 99

Non-Wholly Owned Entities and62

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest - SNG Income Statement Disclosures (Details) - Successor [Member] - SNG [Member] $ in Millions	1 Months Ended
	Sep. 30, 2016USD ($)
Schedule of Equity Method Investments [Line Items]
Revenues	$ 82
Operating income	60
Net income	$ 55

Non-Wholly Owned Entities and63

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest - Equity Method Investments (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Successor [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 1,531
Successor [Member] | SNG [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	1,414
Successor [Member] | Triton [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	45
Successor [Member] | Horizon Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	31
Successor [Member] | Atlantic Coast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	23
Successor [Member] | PennEast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	17
Successor [Member] | Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 1
Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		$ 80
Predecessor [Member] | SNG [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		0
Predecessor [Member] | Triton [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		49
Predecessor [Member] | Horizon Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		14
Predecessor [Member] | Atlantic Coast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		7
Predecessor [Member] | PennEast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		9
Predecessor [Member] | Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		$ 1

Non-Wholly Owned Entities and64

Non-Wholly Owned Entities and Redeemable Noncontrolling Interest - Income from Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2015
Successor [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment	$ 29
Successor [Member] | SNG [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment	27
Successor [Member] | Triton [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment	1
Successor [Member] | Atlantic Coast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment	1
Successor [Member] | Horizon Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment	$ 0
Predecessor [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment		$ 2	$ 2	$ 4
Predecessor [Member] | SNG [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment		0	0	0
Predecessor [Member] | Triton [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment		2	1	3
Predecessor [Member] | Atlantic Coast Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment		0	0	0
Predecessor [Member] | Horizon Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investment		$ 0	$ 1	$ 1