Employee Benefit Plans - Plan Amendments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Pension Plan | U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cost of equalization, percent of defined benefit plan obligation (percent)	1.20%
Amortization to prior service cost, period (years)	24 years
Annual amortization to prior service cost	$ 2
Pension Plan | U.K. | United Kingdom, Pounds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cost of equalization	33
Pension Plan | United States | United States of America, Dollars
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cost of equalization	42
Other Postretirement Benefits Plan | Canada
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation, increase (decrease) for plan amendment	(19)
Other Postretirement Benefits Plan | United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation, increase (decrease) for plan amendment	283
Benefit obligation, increase (decrease) for plan amendment	216
Actuarial gain, increase (decrease) for plan amendment	$ 67