Callaway Energy Center Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Nuclear Waste Matters [Line Items]
Cost	$ 387	$ 361
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	323	256
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	10
Fair Value	704	607
Debt Securities
Nuclear Waste Matters [Line Items]
Cost	228	197
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	5	3
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	1	4
Fair Value	232	196
Equity Securities
Nuclear Waste Matters [Line Items]
Cost	155	161
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	318	253
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	5	6
Fair Value	468	408
Cash
Nuclear Waste Matters [Line Items]
Cost	2	1
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	2	1
Other Debt And Equity Securities
Nuclear Waste Matters [Line Items]
Cost	2	2
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	$ 2	$ 2

[Line Items] for Nuclear Waste Matters [Table]

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled.

+ References

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-Publisher FASB
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