Employee Benefit Plans - Funded Status of Plan (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
United Kingdom
Funded status:
Funded status at end of year	$ 63	$ 85
Funded status recognized in balance sheet:
Long-term assets	63	85
Current liabilities	0	0
Long-term liabilities	0	0
Net amount recognized	63	85
Plans with projected and accumulated benefit obligation in excess of plan assets:
Projected and accumulated benefit obligation	0	0
Fair value of plan assets	0	0
Qualified Plan | United States
Funded status:
Funded status at end of year	(7)	21
Funded status recognized in balance sheet:
Long-term assets	0	21
Current liabilities	0	0
Long-term liabilities	(7)	0
Net amount recognized	(7)	21
Plans with projected and accumulated benefit obligation in excess of plan assets:
Projected and accumulated benefit obligation	1,589	0
Fair value of plan assets	1,582	0
Nonqualified Plan | United States
Funded status:
Funded status at end of year	(70)	(78)
Funded status recognized in balance sheet:
Long-term assets	0	0
Current liabilities	(5)	(6)
Long-term liabilities	(65)	(72)
Net amount recognized	(70)	(78)
Plans with projected and accumulated benefit obligation in excess of plan assets:
Projected and accumulated benefit obligation	70	78
Fair value of plan assets	$ 0	$ 0