Accumulated Other Comprehensive Income (Loss) (Income (Expense) Effect of Reclassifications) (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2014	[1]	Sep. 30, 2014	[1]	Jun. 30, 2014	[1]	Mar. 31, 2014	[1]	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Affected Line Item on the Statements of Income [Line Items]
Energy purchases																	$ (855)	$ (924)	$ (856)
Interest Expense																	(871)	(843)	(778)
Other Income (Expense) - net																	108	105	(55)
Total Pre-tax																	2,068	2,129	1,728
Income Taxes																	(465)	(692)	(360)
Total After-Tax	$ 405		$ 396		$ 250		$ 552		$ 408		$ 410		$ 230		$ 389		1,603	1,437	1,368
Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total After-Tax																	(145)	(45)
Available For Sale Securities [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Other Income (Expense) - net																	4	13
Total Pre-tax																	4	13
Income Taxes																	(2)	(7)
Total After-Tax																	2	6
Qualifying Derivatives [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax																	(17)	87
Income Taxes																	15	(23)
Total After-Tax																	(2)	64
Qualifying Derivatives [Member] | Interest Rate Swaps [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Interest Expense																	(11)	(16)
Discontinued operations																	(77)	0
Qualifying Derivatives [Member] | Cross Currency Swaps [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Interest Expense																	2	4
Other Income (Expense) - net																	49	57
Qualifying Derivatives [Member] | Commodity Contracts [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Discontinued operations																	20	42
Equity Investees Accumulated Other Comprehensive Income [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Other Income (Expense) - net																	1	0
Total Pre-tax																	1	0
Income Taxes																	0	0
Total After-Tax																	1	0
Defined Benefit Plans [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax																	(192)	(152)
Income Taxes																	46	37
Total After-Tax																	(146)	(115)
Defined Benefit Plans [Member] | Prior Service Costs [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax																	0	(7)
Defined Benefit Plans [Member] | Net Actuarial Loss [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member]
Affected Line Item on the Statements of Income [Line Items]
Total Pre-tax																	(192)	(145)
Kentucky Utilities Co [Member]
Affected Line Item on the Statements of Income [Line Items]
Energy purchases																	(18)	(23)	(22)
Interest Expense																	(82)	(77)	(70)
Other Income (Expense) - net																	1	(1)	(3)
Total Pre-tax																	374	355	360
Income Taxes																	$ (140)	$ (135)	$ (132)

[1] Quarterly results can vary depending on, among other things, weather . Accordingly, comparisons among quarters of a year may not be indicative of overall tr ends and changes in operations.