Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Interest carryforwards		$ 196
U.K.
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 541	675
Interest carryforwards	400	415
Interest carryforwards	53	0
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	2	36
Interest carryforwards	367	0
Interest carryforwards	424	0
U.S. State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	315	412
Interest carryforwards	221	0
Interest carryforwards	227	0
Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	369	392
Interest carryforwards	30	36
Interest carryforwards	$ 186	$ 196