Fair Value Measurements (Details 3) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	$ 1,776	$ 1,778
Unrealized Gain	44	16
Fair Value	1,820	1,794
Equity securities
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities
Cost Basis	576	542
Unrealized Gains	52	34
Fair Value	628	576
FES \| Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost Basis	825	801
Unrealized Gain	26	9
Fair Value	851	810
FES \| Equity securities
Amortized cost basis, unrealized gains and losses and fair values of investments in available-for-sale securities
Cost Basis	372	354
Unrealized Gains	36	24
Fair Value	$ 408	$ 378

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