Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities
Net (Loss)/Income	$ (891)	$ (6,436)	$ 132
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Equity in earnings and distribution of unconsolidated affiliates	54	37	49
Depreciation and amortization	1,367	1,566	1,523
Provision for bad debts	48	64	64
Amortization of nuclear fuel	49	45	46
Amortization of financing costs and debt discount/premiums	3	(11)	(12)
Adjustment to loss/(gain) on debt extinguishment	21	(75)	25
Gain (Loss) on Extinguishment of Debt	(142)	75	(95)
Amortization of intangibles and out-of-market contracts	91	81	64
Amortization of unearned equity compensation	10	41	42
Net (gain)/loss on sale of assets and equity method investments	(224)	14	(4)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	0	(21)	0
Impairment losses	1,186	5,086	97
Changes in derivative instruments	23	233	(61)
Changes in deferred income taxes and liability for uncertain tax benefits	(43)	1,326	(154)
Changes in Collateral Deposits Supporting Energy Risk Management Activities	365	(381)	146
Gain on sale of emissions allowances	47	0	0
Changes in nuclear decommissioning trust liability	41	(2)	19
Cash provided/(used) by changes in other working capital, net of acquisition and disposition effects:
Accounts receivable - trade	(12)	136	(2)
Inventory	134	(26)	(245)
Prepayments and other current assets	(39)	8	36
Accounts payable	(27)	(218)	(12)
Accrued expenses and other current liabilities	(39)	(9)	(26)
Other assets and liabilities	(92)	(149)	(217)
Net Cash Provided by Operating Activities	2,072	1,309	1,510
Cash Flows from Investing Activities
Acquisition of businesses, net of cash acquired	(209)	(31)	(2,936)
Capital expenditures	(1,244)	(1,283)	(909)
(Increase)/decrease in restricted cash, net	(29)	8	57
(Increase)/decrease in restricted cash to support equity requirements for U.S. DOE funded projects	(3)	35	(206)
Increase (Decrease) in Notes Receivables	17	18	25
Proceeds from renewable energy grants	36	82	916
Purchases of emission allowances, net of proceeds	(1)	41	(16)
Investments in nuclear decommissioning trust fund securities	(551)	(629)	(619)
Proceeds from sales of nuclear decommissioning trust fund securities	510	631	600
Proceeds from sale of assets, net	636	27	203
Investments in unconsolidated affiliates	(34)	(395)	(103)
Other	48	11	85
Net Cash Used by Investing Activities	(824)	(1,485)	(2,903)
Cash Flows from Financing Activities
Payments of dividends to preferred and common stockholders	(76)	(201)	(196)
Net receipts from settlement of acquired derivatives that include financing elements	151	196	9
Payments for treasury stock	0	(437)	(39)
Payments for Repurchase of Redeemable Preferred Stock	(226)	0	0
Distributions from, net of contributions to, noncontrolling interests in subsidiaries	(156)	47	189
Proceeds from sale of noncontrolling interests in subsidiaries	0	600	630
Proceeds from issuance of common stock	1	1	21
Proceeds from issuance of long-term debt	5,527	1,004	4,563
Payments of debt issuance and hedging costs	(89)	(21)	(67)
Payments for short and long-term debt	(5,913)	(1,599)	(3,827)
Proceeds from (Payments for) Other Financing Activities	(13)	(22)	(18)
Net Cash (Used)/Provided by Financing Activities	(794)	(432)	1,265
Effect of exchange rate changes on cash and cash equivalents	1	10	(10)
Net Increase/(Decrease) in Cash and Cash Equivalents	455	(598)	(138)
Cash and Cash Equivalents at Beginning of Period	1,518	2,116	2,254
Cash and Cash Equivalents at End of Period	$ 1,973	$ 1,518	$ 2,116