Severance and Leased Real Estate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Employee Severance
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 19	$ 5
Accrued to expense	6	33
Payments, net	(16)	(19)
Restructuring reserve, ending balance	$ 9	$ 19
Accounting Standards Update 2016-02
Restructuring Cost and Reserve [Line Items]
Capital lease obligations			$ 47