Taxation (Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, beginning of year	$ 17	$ 16
Additions based on tax provisions related to the current year	3	3
Additions based on tax positions related to prior years	0	2
Reductions for tax positions of prior years	(4)	(4)
Reductions for the lapse of the applicable statutes of limitations	(3)	0
Unrecognized Tax Benefits, end of year	$ 13	$ 17