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Fair Value Measurements (Reconciliation of Change in Fair Value of Derivatives, Significant Unobservable Inputs) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Realized and unrealized gains (losses): |  |  |
Realized and unrealized gains (losses) reflected in operating revenues | $ 379 | $ 397 | $ 462
Unrealized gains (losses) reflected in operating revenues, for derivatives still held at the reporting date | 281 | 283 | 289
Derivative Financial Instruments, Net [Member] |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Fair value of derivatives based on significant unobservable inputs beginning balance | 578 | 538 | 622
Realized and unrealized gains (losses): |  |  |
Realized and unrealized gains (losses) included in earnings | 376 | 333 | 451
Realized and unrealized gains (losses) included in other comprehensive income (loss) | (18) | 8 | 11
Realized and unrealized gains (losses) included in regulatory assets and liabilities | 0 | 1 | 3
Purchases | 126 | 261 | 180
Settlements | (317) | (390) | (473)
Issuances | (197) | (195) | (202)
Transfers in(c) | 17 | 19 | (13)
Transfers out(c) | 1 | 3 | (41)
Fair value of derivatives based on significant unobservable inputs ending balance | 566 | 578 | 538
The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to derivatives still held at the reporting date(d) | 277 | 219 | 277
FPL[Member] | Derivative Financial Instruments, Net [Member] |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Fair value of derivatives based on significant unobservable inputs beginning balance | 1 | 0 | 5
Realized and unrealized gains (losses): |  |  |
Realized and unrealized gains (losses) included in earnings | 0 | 0 | 0
Realized and unrealized gains (losses) included in other comprehensive income (loss) | 0 | 0 | 0
Realized and unrealized gains (losses) included in regulatory assets and liabilities | 0 | 1 | 3
Purchases | 0 | 0 | 0
Settlements | (1) | 0 | (8)
Issuances | 0 | 0 | 0
Transfers in(c) | 0 | 0 | 0
Transfers out(c) | 0 | 0 | 0
Fair value of derivatives based on significant unobservable inputs ending balance | 0 | 1 | 0
The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to derivatives still held at the reporting date(d) | $ 0 | $ 0 | $ 0

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- Definition This element represents total gains or losses for the period (realized and unrealized), arising from net assets (liabilities) measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in regulatory assets and liabilities. + References No definition available. + Details
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- Definition This element represents total gains or losses for the period (realized and unrealized), arising from net assets (liabilities) measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset (liability) value. + References No definition available. + Details
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- Definition This element represents the net asset (liability) fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. + References No definition available. + Details
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- Definition This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in Earnings. Such unrealized (holding) gains or losses relate to those assets (liabilities) still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3). + References No definition available. + Details
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- Definition This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in Operating Revenues. Such unrealized (holding) gains or losses relate to those assets (liabilities) still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3). + References No definition available. + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets) in operating revenues; the fair value of which assets was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References No definition available. + Details
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- Definition Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of gain (loss) recognized in other comprehensive income, arising from assets, liabilities and financial instruments classified in shareholders' equity measured at fair value on a recurring basis using unobservable inputs (level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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