Property, Plant, and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, plant and equipment

The registrants' property, plant, and equipment in service consisted of the following at December 31, 2018 and 2017:

At December 31, 2018:	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Electric utilities:
Generation	$	52,324	$	16,533	$	19,145	$	2,849	$	13,246	$	—
Transmission	11,344		4,380		6,156		769		—		—
Distribution	18,746		7,389		10,389		968		—		—
General/other	4,446		2,100		1,985		314		25		—
Electric utilities' plant in service	86,860		30,402		37,675		4,900		13,271		—
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	12,409		—		—		—		—		12,409
Storage facilities	1,640		—		—		—		—		1,640
Other	1,128		—		—		—		—		1,128
Southern Company Gas plant in service	15,177		—		—		—		—		15,177
Other plant in service	1,669		—		—		—		—		—
Total plant in service	$	103,706	$	30,402	$	37,675	$	4,900	$	13,271	$	15,177

At December 31, 2017:	Southern Company		Alabama Power		Georgia Power		Mississippi Power		Southern Power		Southern Company Gas
	(in millions)
Electric utilities:
Generation	$	51,279	$	14,213	$	17,038	$	2,801	$	13,737	$	—
Transmission	11,562		4,119		5,947		737		—		—
Distribution	19,239		7,034		9,978		946		—		—
General/other	4,402		1,960		1,898		289		18		—
Electric utilities' plant in service	86,482		27,326		34,861		4,773		13,755		—
Southern Company Gas:
Natural gas distribution utilities transportation and distribution	13,079		—		—		—		—		13,079
Storage facilities	1,599		—		—		—		—		1,599
Other	1,155		—		—		—		—		1,155
Southern Company Gas plant in service	15,833		—		—		—		—		15,833
Other plant in service	1,227		—		—		—		—		—
Total plant in service	$	103,542	$	27,326	$	34,861	$	4,773	$	13,755	$	15,833

The primary assets in Southern Power's property, plant, and equipment are generating facilities, which generally have estimated useful lives as follows:

Southern Power Generating Facility	Useful life
Natural gas	Up to 45 years
Biomass	Up to 40 years
Solar	Up to 35 years
Wind	Up to 30 years

Assets acquired under a capital lease

Assets acquired under a capital lease are included in property, plant, and equipment and are further detailed in the table below for the applicable registrants:

	Southern Company			Georgia Power
	(in millions)
At December 31, 2018:
Office buildings	$	216		$	61
PPAs(*)	—			144
Computer-related equipment	43			—
Gas pipeline	7			—
Less: Accumulated amortization	(75		)	(84		)
Balance, net of amortization	$	191		$	121
At December 31, 2017:
Office buildings	$	216		$	61
PPAs(*)	—			144
Computer-related equipment	51			—
Gas pipeline	6			—
Less: Accumulated amortization	(72		)	(68		)
Balance, net of amortization	$	201		$	137

(*) Represents Georgia Power's affiliate PPAs with Southern Power. See Note 1 under "Affiliate Transactions" and Note 9 under "Fuel and Power Purchase Agreements – Affiliate" for additional information.

Composite straight-line rates

Transportation costs under these agreements in 2018, 2017, and 2016 were as follows:

	Alabama Power		Georgia Power		Southern Power		Southern Company Gas
	(in millions)
2018	$	8	$	101	$	25	$	32
2017	9		102		25		32
2016(*)	2		35		7		15

(*) Represents costs incurred for the period subsequent to Southern Company Gas' investment in SNG.

On November 16, 2018, SNG completed its purchase of Georgia Power's natural gas lateral pipeline serving Plant McDonough Units 4 through 6 at net book value, as approved by the Georgia PSC on January 16, 2018. SNG expects to pay $142 million to Georgia Power in the first quarter 2020. During the interim period, Georgia Power will receive a discounted shipping rate to reflect the delayed consideration. Southern Company Gas' portion of the expected capital expenditures for the purchase of this pipeline and additional construction is $122 million.

SCS, as agent for the traditional electric operating companies and Southern Power, has agreements with certain subsidiaries of Southern Company Gas to purchase natural gas. Natural gas purchases made under these agreements were immaterial for Alabama Power and Mississippi Power and as follows for Georgia Power and Southern Power in 2018, 2017, and 2016:

	Georgia Power		Southern Power
	(in millions)
2018	$	21	$	119
2017	22		119
2016(*)	10		17

(*) Represents costs incurred for the period subsequent to Southern Company's acquisition of Southern Company Gas.

Mississippi Power's and Southern Power's total power purchased from affiliates through the power pool is included in purchased power on their respective statements of income and was as follows:

	Mississippi Power		Southern Power
	(in millions)
2018	$	15	$	41
2017	16		27
2016	29		21

Costs for these services from SCS in 2018, 2017, and 2016 were as follows:

	Alabama Power		Georgia Power		Mississippi Power		Southern Power(a)		Southern Company Gas(b)
	(in millions)
2018	$	508	$	653	$	104	$	98	$	194
2017	479		625		140		218		63
2016	460		606		231		193		17

(a) Prior to December 2017, Southern Power had no employees but was billed for employee-related costs from SCS.

(b) Southern Company Gas' 2016 costs represent services provided subsequent to the Merger.

The approximate rates for 2018, 2017, and 2016 are as follows:

	2018		2017		2016
	(percent)
Alabama Power	3.0	%	2.9	%	3.0	%
Georgia Power	2.6	%	2.7	%	2.8	%
Mississippi Power(*)	4.1	%	3.7	%	4.2	%
Southern Company Gas	2.9	%	2.9	%	2.8	%

(*) Mississippi Power's decrease in 2017 is primarily the result of recording a loss on its lignite mine in June 2017.

Ownership and investment in jointly-owned facilities

At December 31, 2018, the registrants' percentage ownership and investment (exclusive of nuclear fuel) in jointly-owned facilities in commercial operation were as follows:

Facility (Type)	Percent Ownership			Plant in Service		Accumulated Depreciation		CWIP
				(in millions)
Alabama Power
Greene County (natural gas) Units 1 and 2	60.0	%	(a)	$	274	$	71	$	1
Plant Miller (coal) Units 1 and 2	91.8		(b)	2,056		619		138
Georgia Power
Plant Hatch (nuclear)	50.1	%	(c)	$	1,569	$	615	$	54
Plant Vogtle (nuclear) Units 1 and 2	45.7		(c)	3,804		2,150		84
Plant Scherer (coal) Units 1 and 2	8.4		(c)	266		96		14
Plant Scherer (coal) Unit 3	75.0		(c)	1,238		493		66
Plant Wansley (coal)	53.5		(c)	1,179		362		160
Rocky Mountain (pumped storage)	25.4		(d)	184		135		—
Mississippi Power
Greene County (natural gas) Units 1 and 2	40.0	%	(a)	$	180	$	93	$	1
Plant Daniel (coal) Units 1 and 2	50.0		(e)	723		201		7
Southern Company Gas
Dalton Pipeline (natural gas pipeline)	50.0	%	(f)	$	270	$	6	$	—

(a) Jointly owned by Alabama Power and Mississippi Power and operated and maintained by Alabama Power.

(b) Jointly owned with PowerSouth and operated and maintained by Alabama Power.

(c) Georgia Power owns undivided interests in Plants Hatch, Vogtle Units 1 and 2, Scherer, and Wansley in varying amounts jointly with one or more of the following entities: OPC, MEAG Power, Dalton, Florida Power & Light Company, JEA, and Gulf Power. Georgia Power has been contracted to operate and maintain the plants as agent for the co-owners and is jointly and severally liable for third party claims related to these plants.

(d) Jointly owned with OPC, which is the operator of the plant.

(e) Jointly owned by Gulf Power and Mississippi Power. In accordance with the operating agreement, Mississippi Power acts as Gulf Power's agent with respect to the operation and maintenance of these units.

(f) Jointly owned with The Williams Companies, Inc. The Dalton Pipeline is a 115-mile natural gas pipeline that serves as an extension of the Transco natural gas pipeline system into northwest Georgia. Southern Company Gas also entered into an agreement to lease its 50% undivided ownership in the Dalton Pipeline that became effective when it was placed in service in August 2017. Under the lease, Southern Company Gas will receive approximately $26 million annually for an initial term of 25 years. The lessee is responsible for maintaining the pipeline during the lease term and for providing service to transportation customers under its FERC-regulated tariff.