Leases (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Property, Plant and Equipment [Line Items]
Lessee, Operating Lease, Liability, to be Paid		$ (223)
Total consideration			$ 56
Gain (Loss) on Disposition of Assets		0	56	$ 0
Accelerated amortization	$ 28
Present value of lease liabilities		210	306		$ 325
Operating Lease, Operating, Short-term and Variable Leases, Cost		83
Finance Lease, Interest Expense		17	$ 4
Finance Lease, Principal Payments		16
Operating and Variable Lease Costs		$ 130
Operating Lease, Weighted Average Discount Rate, Percent		2.50%	3.30%
Finance Lease, Weighted Average Discount Rate, Percent		3.00%	3.00%
Operating Lease, Weighted Average Remaining Lease Term		3 years	3 years
Finance Lease, Weighted Average Remaining Lease Term		19 years	20 years
Operating Lease Liability, Prior Headquarters		$ 13