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Employee Retirement Benefits - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Target asset allocations [Abstract] |  |  |
Defined contribution expense | $ 53 | $ 52 | $ 63
Other Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | 241 | 325 |
Pension Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | $ 1,427 | $ 1,177 |
Weighted-average assumptions used to determine benefit obligations [Abstract] |  |  |
Discount rate (in hundredths) | 3.59% | 4.09% |
Salary increase (in hundredths) | 4.10% | 4.10% |
Pension Benefits [Member] | Equity Securities [Member] |  |  |
Target asset allocations [Abstract] |  |  |
Equity investments, target allocation percentage (in hundredths) | 45.00% |  |
Pension Benefits [Member] | Debt Securities [Member] |  |  |
Target asset allocations [Abstract] |  |  |
Equity investments, target allocation percentage (in hundredths) | 32.00% |  |
Pension Benefits [Member] | Alternative Investments [Member] |  |  |
Target asset allocations [Abstract] |  |  |
Equity investments, target allocation percentage (in hundredths) | 13.00% |  |
Pension Benefits [Member] | Convertible Securities [Member] |  |  |
Target asset allocations [Abstract] |  |  |
Equity investments, target allocation percentage (in hundredths) | 10.00% |  |
FPL[Member] |  |  |
Target asset allocations [Abstract] |  |  |
Defined contribution expense | $ 33 | $ 32 | $ 40
FPL[Member] | Other Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | 208 | 222 |
FPL[Member] | Pension Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan | $ 1,351 | $ 1,301 |

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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