Drilling Fleet (Disposal) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dispositions
Net cash proceeds from sale of assets	$ 30	$ 54	$ 250
Gain (loss) on the sale of assets	4	(36)	(26)
Rig sales
Dispositions
Net cash proceeds from sale of assets	22	35	185
Gain (loss) on the sale of assets	$ 13	14	(1)
Gain on the sale of assets, net of tax		$ 11
Gain (loss) on the sale of assets per diluted share	$ 0.04	$ 0.02
Sale of other assets
Dispositions
Net cash proceeds from sale of assets	$ 8	$ 16	30
Gain (loss) on the sale of assets	(9)	(50)	$ (25)
Assets held for sale
Dispositions
Aggregate carrying amount of assets held for sale	$ 6	$ 8