Leases (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Property, Plant and Equipment [Line Items]
Build-to-suit lease liability		$ (327)
Total consideration		56
Gain (Loss) on Disposition of Assets		56	$ 0	$ 0
Accelerated amortization	$ 28	28
Present value of lease liabilities		306			$ 325
Operating Lease, Operating, Short-term and Variable Leases, Cost		103
Interest on lease liability		4
Finance Lease, Principal Payments		1
Operating and Variable Lease Costs		$ 180
Operating lease, weighted average discount rate		3.30%
Finance lease, weighted average discount rate		3.00%
Operating Lease, Weighted Average Remaining Lease Term		3 years
Finance Lease, Weighted Average Remaining Lease Term		20 years
Operating Lease, Lease Not yet Commenced, Amount		$ 38
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract		4 years
ASU 2016-02
Property, Plant and Equipment [Line Items]
Capitalized construction costs					217
Build-to-suit lease liability					$ 219
Former Corporate Headquarters [Member]
Property, Plant and Equipment [Line Items]
Present value of lease liabilities		$ 27