Operating Segments, Geographic Analysis and Major Customers (Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Operating segments, geographical analysis and major customers
Long-lived assets	$ 19,416	$ 20,408
U.S.
Operating segments, geographical analysis and major customers
Long-lived assets	6,259	6,257
Norway
Operating segments, geographical analysis and major customers
Long-lived assets	3,203	3,260
Greece
Operating segments, geographical analysis and major customers
Long-lived assets	2,760	1,103
Other countries
Operating segments, geographical analysis and major customers
Long-lived assets	$ 7,194	$ 9,788