v3.10.0.1
Financial information by segment, Assets and liabilities by business sector (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Assets [Abstract]        
Contracted concessional assets $ 8,736,368 $ 9,084,270    
Investments carried under the equity method 53,002 55,784    
Current financial investments 215,148 210,138    
Cash and cash equivalents (project companies) 657,212 669,387 $ 614,312 $ 594,811
Total assets 10,157,276 10,492,339    
Liabilities [Abstract]        
Long-term and short-term project debt 5,218,820 5,475,208    
Grants and other liabilities 1,662,379 1,636,060    
Long-term and short-term corporate debt 639,041 643,083    
Total liabilities 8,293,042 8,596,886    
Equity 1,864,234 1,895,453 $ 2,013,130 $ 1,959,111
Total liabilities and equity 10,157,276 10,492,339    
Renewable Energy [Member]        
Assets [Abstract]        
Contracted concessional assets 7,165,843 7,436,362    
Investments carried under the equity method 12,088 12,419    
Current financial investments 20,478 17,249    
Cash and cash equivalents (project companies) 455,421 452,792    
Total assets 7,653,830 7,918,822    
Liabilities [Abstract]        
Long-term and short-term project debt 3,958,261 4,162,596    
Grants and other liabilities 1,659,756 1,635,508    
Total liabilities 5,618,017 5,798,104    
Efficient Natural Gas [Member]        
Assets [Abstract]        
Contracted concessional assets 606,883 660,387    
Investments carried under the equity method 0 0    
Current financial investments 118,323 116,430    
Cash and cash equivalents (project companies) 26,560 39,064    
Total assets 751,766 815,881    
Liabilities [Abstract]        
Long-term and short-term project debt 548,223 579,173    
Grants and other liabilities 788 552    
Total liabilities 549,011 579,725    
Electric Transmission Lines [Member]        
Assets [Abstract]        
Contracted concessional assets 876,477 897,269    
Investments carried under the equity method 0 0    
Current financial investments 61,117 59,289    
Cash and cash equivalents (project companies) 14,712 15,325    
Total assets 952,306 971,883    
Liabilities [Abstract]        
Long-term and short-term project debt 680,398 698,346    
Grants and other liabilities 1,032 0    
Total liabilities 681,430 698,346    
Water [Member]        
Assets [Abstract]        
Contracted concessional assets 87,165 90,252    
Investments carried under the equity method 40,914 43,365    
Current financial investments 14,460 14,577    
Cash and cash equivalents (project companies) 8,248 13,681    
Total assets 150,787 161,875    
Liabilities [Abstract]        
Long-term and short-term project debt 31,938 35,093    
Grants and other liabilities 803 0    
Total liabilities 32,741 35,093    
Allocated [Member]        
Assets [Abstract]        
Contracted concessional assets 8,736,368 9,084,270    
Investments carried under the equity method 53,002 55,784    
Current financial investments 214,378 207,545    
Cash and cash equivalents (project companies) 504,941 520,862    
Total assets 9,508,689 9,868,461    
Liabilities [Abstract]        
Long-term and short-term project debt 5,218,820 5,475,208    
Grants and other liabilities 1,662,379 1,636,060    
Total liabilities 6,881,199 7,111,268    
Unallocated [Member]        
Assets [Abstract]        
Other non-current assets 216,771 210,378    
Other current assets (including cash and cash equivalents at holding company level) 431,816 413,500    
Total assets 648,587 623,878    
Liabilities [Abstract]        
Long-term and short-term corporate debt 639,041 643,083    
Other non-current liabilities 591,456 657,345    
Other current liabilities 181,346 185,190    
Total liabilities 1,411,843 1,485,618    
Equity 1,864,234 1,895,453    
Total liabilities and equity $ 3,276,077 $ 3,381,071