Debt (Schedule of Line of Credit Facilities) (Details) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 880
Syndicated Credit Facility $850 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date		Aug. 31, 2023
Line of Credit Facility, Maximum Borrowing Capacity		$ 850
Long-term Line of Credit	[1]	$ 20	$ 18
Line of Credit Facility, Interest Rate Description		Senior unsecured long-term debt rating
Credit Facility $100 Million 2022 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date		Mar. 31, 2022
Line of Credit Facility, Maximum Borrowing Capacity			100
Long-term Line of Credit	[1]	$ 99	0
Line of Credit Facility, Interest Rate Description		Fixed
Credit Facility 100 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date		May 30, 2023
Line of Credit Facility, Maximum Borrowing Capacity		$ 100
Long-term Line of Credit	[1]	$ 61	61
Line of Credit Facility, Interest Rate Description		Fixed
Syndicated Credit Facility $75 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date		Jun. 30, 2021
Line of Credit Facility, Maximum Borrowing Capacity			75
Long-term Line of Credit	[1]	$ 15	34
Line of Credit Facility, Interest Rate Description		Fixed
Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date	[2]	Dec. 31, 2021
Line of Credit Facility, Maximum Borrowing Capacity		$ 105
Long-term Line of Credit	[1],[2]	$ 105	106
Line of Credit Facility, Interest Rate Description		Fixed
Syndicated Credit Facility $500 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date		May 31, 2022
Line of Credit Facility, Maximum Borrowing Capacity		$ 500
Long-term Line of Credit	[1]	$ 375	$ 395
Line of Credit Facility, Interest Rate Description		Debt rating and utilization %

[1] Represents issued but undrawn letters of credit. There was no cash borrowed for the periods presented.

[2] Foreign currency denominated facility, amounts presented are in U.S. dollars.