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Fair Value Measurements (Details 3) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	$ 1,746	$ 1,735
Unrealized Gain	38	38
Fair Value	1,784	1,773
Equity securities
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities
Cost Basis	852	822
Unrealized Gains	130	103
Fair Value	982	925
FES | Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	855	847
Unrealized Gain	28	27
Fair Value	883	874
FES | Equity securities
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities
Cost Basis	578	564
Unrealized Gains	89	70
Fair Value	$ 667	$ 634

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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.

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