Drilling Fleet (Disposal) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Dispositions
Net cash proceeds from sale of assets	$ 6	$ 1
Gain (loss) on the sale of assets	(59)	$ (1)
Assets sold, not discontinued operations | Rig sales
Dispositions
Net cash proceeds from sale of assets	4
Gain (loss) on the sale of assets	$ (60)
Gain (loss) on the sale of assets per diluted share	$ (0.10)
Gain (loss) on disposal of assets, tax effect	$ 0