Operating Segments, Geographic Analysis and Major Customers (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating segments, geographical analysis and major customers
Number of operating segments | segment									1
Operating revenues	$ 974	$ 906	$ 940	$ 1,341	$ 1,851	$ 1,608	$ 1,884	$ 2,043	$ 4,161	$ 7,386	$ 9,185
U.S.
Operating segments, geographical analysis and major customers
Operating revenues									1,977	2,416	2,410
U.K.
Operating segments, geographical analysis and major customers
Operating revenues									551	1,139	1,194
Brazil
Operating segments, geographical analysis and major customers
Operating revenues									453	673	651
Norway
Operating segments, geographical analysis and major customers
Operating revenues									214	650	1,036
Other countries
Operating segments, geographical analysis and major customers
Operating revenues									$ 966	$ 2,508	$ 3,894