Jointly Owned Facilities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Jointly Owned Facilities [Line Items]
Percentage of leasehold interest in Colstrip Units 1 and 2		50.00%
Percentage of leasehold interest in Colstrip Unit 3		30.00%
Percentage of interest by Northwestern in Colstrip Unit 4	30.00%	30.00%
Proportionate share by each party of operating and construction costs regarding Colstrip Unit 3 or 4	15.00%	15.00%
Susquehanna Nuclear Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	90.00%	90.00%
Electric plant	$ 4,686	$ 4,628
Accumulated depreciation	3,545	3,530
Construction work in progress	76	65
Conemaugh Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	16.25%	16.25%
Electric plant	247	238
Accumulated depreciation	131	122
Construction work in progress	63	30
Keystone Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	12.34%	12.34%
Electric plant	207	206
Accumulated depreciation	91	82
Construction work in progress	2	3
Trimble County Units 1 and 2 Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	75.00%	75.00%
Electric plant	1,288	1,279
Accumulated depreciation	144	112
Construction work in progress	54	43
Merrill Creek Reservoir [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	8.37%	8.37%
Other property	22	22
Accumulated depreciation	16	15
PPL Energy Supply LLC [Member]
Jointly Owned Facilities [Line Items]
Percentage of leasehold interest in Colstrip Units 1 and 2		50.00%
Percentage of leasehold interest in Colstrip Unit 3		30.00%
Percentage of interest by Northwestern in Colstrip Unit 4	30.00%	30.00%
Proportionate share by each party of operating and construction costs regarding Colstrip Unit 3 or 4	15.00%	15.00%
PPL Energy Supply LLC [Member] | Susquehanna Nuclear Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	90.00%	90.00%
Electric plant	4,686	4,628
Accumulated depreciation	3,545	3,530
Construction work in progress	76	65
PPL Energy Supply LLC [Member] | Conemaugh Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	16.25%	16.25%
Electric plant	247	238
Accumulated depreciation	131	122
Construction work in progress	63	30
PPL Energy Supply LLC [Member] | Keystone Generation Plant [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	12.34%	12.34%
Electric plant	207	206
Accumulated depreciation	91	82
Construction work in progress	2	3
PPL Energy Supply LLC [Member] | Merrill Creek Reservoir [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	8.37%	8.37%
Other property	22	22
Accumulated depreciation	16	15
LG And E And KU Energy LLC [Member] | Trimble County Unit 1 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	75.00%	75.00%
Electric plant	308	304
Other property
Accumulated depreciation	42	33
Construction work in progress	18	10
LG And E And KU Energy LLC [Member] | Trimble County Unit 2 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	75.00%	75.00%
Electric plant	980	975
Other property
Accumulated depreciation	102	79
Construction work in progress	36	33
Louisville Gas And Electric Co [Member] | E W Brown Units 6 And 7 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	38.00%	38.00%
Electric plant	40	40
Other property
Accumulated depreciation	7	5
Construction work in progress	1
Louisville Gas And Electric Co [Member] | Paddys Run Unit 13 And E W Brown Unit 5 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	53.00%	53.00%
Electric plant	46	46
Other property
Accumulated depreciation	5	3
Construction work in progress	1
Louisville Gas And Electric Co [Member] | Trimble County Unit 1 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	75.00%	75.00%
Electric plant	308	304
Other property
Accumulated depreciation	42	33
Construction work in progress	18	10
Louisville Gas And Electric Co [Member] | Trimble County Unit 2 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	14.25%	14.25%
Electric plant	200	198
Other property
Accumulated depreciation	19	14
Construction work in progress	14	13
Louisville Gas And Electric Co [Member] | Trimble County Units 5 And 6 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	29.00%	29.00%
Electric plant	29	29
Other property
Accumulated depreciation	3	2
Construction work in progress
Louisville Gas And Electric Co [Member] | Trimble County Units 7 Through 10 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	37.00%	37.00%
Electric plant	69	68
Other property
Accumulated depreciation	7	6
Construction work in progress	1	2
Louisville Gas And Electric Co [Member] | Cane Run Unit 7 Combined Cycle Gas Turbine [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	22.00%	22.00%
Electric plant
Other property
Accumulated depreciation
Construction work in progress	91	16
Louisville Gas And Electric Co [Member] | Green River Unit Five Combined Cycle Gas Turbine [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	40.00%
Electric plant
Accumulated depreciation
Construction work in progress	1
Kentucky Utilities Co [Member] | E W Brown Units 6 And 7 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	62.00%	62.00%
Electric plant	64	64
Other property
Accumulated depreciation	11	7
Construction work in progress	2	1
Kentucky Utilities Co [Member] | Paddys Run Unit 13 And E W Brown Unit 5 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	47.00%	47.00%
Electric plant	42	42
Other property
Accumulated depreciation	4	2
Construction work in progress	1
Kentucky Utilities Co [Member] | Trimble County Unit 2 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	60.75%	60.75%
Electric plant	780	777
Other property
Accumulated depreciation	83	65
Construction work in progress	22	20
Kentucky Utilities Co [Member] | Trimble County Units 5 And 6 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	71.00%	71.00%
Electric plant	70	70
Other property
Accumulated depreciation	8	4
Construction work in progress
Kentucky Utilities Co [Member] | Trimble County Units 7 Through 10 [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	63.00%	63.00%
Electric plant	118	116
Other property
Accumulated depreciation	12	10
Construction work in progress	2	2
Kentucky Utilities Co [Member] | Cane Run Unit 7 Combined Cycle Gas Turbine [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	78.00%	78.00%
Electric plant
Other property
Accumulated depreciation
Construction work in progress	317	53
Kentucky Utilities Co [Member] | Green River Unit Five Combined Cycle Gas Turbine [Member]
Jointly Owned Facilities [Line Items]
Ownership interest	60.00%
Electric plant
Other property
Accumulated depreciation
Construction work in progress	$ 2