Workforce Reduction Plan (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 24	$ 25	$ 86
Plan curtailment cost			20
Special termination cost			$ 49
Agreement Positions [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | item		140	250
Management Positions [Member]
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | item	540	330	460
Compensation and benefits expense [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 22	$ 23	$ 12
Compensation and benefits expense [Member] | Equity Compensation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2	$ 2	5
Other Income [Member] | Pension. [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 69