Business Segments - Revenue by Shipping Location and Long-lived Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 8,782	$ 10,381	$ 9,138
Long-lived assets	4,063	5,153	5,866
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	4,609	4,689	4,311
Long-lived assets	1,703	2,367	2,670
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	1,200	964	822
Long-lived assets	221	219	197
Norway
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	776	952	684
Long-lived assets	1,314	1,627	1,953
Other foreign countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	2,197	3,776	3,321
Long-lived assets	$ 825	$ 940	$ 1,046