Debt (Schedule of Line of Credit Facilities) (Details) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 1,132
Syndicated Credit Facility $850 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		850
Long-term Line of Credit	[1]	$ 21	$ 20
Line of Credit Facility, Interest Rate Description		Senior unsecured long-term debt rating
Credit Facility 100 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 100
Long-term Line of Credit	[1]	$ 75	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, Maximum Borrowing Capacity		$ 75
Long-term Line of Credit	[1]	$ 51	15
Line of Credit Facility, Interest Rate Description		Fixed
Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[2]	$ 100
Long-term Line of Credit	[1],[2]	$ 100	105
Line of Credit Facility, Interest Rate Description	[2]	Fixed
Syndicated Credit Facility $500 Million [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 500
Long-term Line of Credit	[1]	$ 210	375
Line of Credit Facility, Interest Rate Description		Debt rating and utilization %
Credit Facility $150 Million
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 150
Long-term Line of Credit	[1]	$ 150	0
Line of Credit Facility, Interest Rate Description		Fixed
Credit Facility $100 Million 2021
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 100
Long-term Line of Credit	[1]	$ 100	0
Line of Credit Facility, Interest Rate Description		Fixed
Credit Facility $107 Million
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 107
Long-term Line of Credit	[1]	$ 107	$ 99
Line of Credit Facility, Interest Rate Description		Fixed

[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.