Restructuring and Asset Impairment Charges (Schedule of Restructuring Charges) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Charged to Costs and Expenses	$ 17	$ 18	$ 31
Restructuring charges incurred to date	350
2020-2021 Cost Savings Restructuring Program
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance	0
Charged to Costs and Expenses	15
Payments and Other	(10)
Ending Reserve Balance	5	0
Restructuring charges incurred to date	16
2020-2021 Cost Savings Restructuring Program | Branch closure charges
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance	0
Charged to Costs and Expenses	7
Payments and Other	(4)
Ending Reserve Balance	3	0
Restructuring charges incurred to date	8
2020-2021 Cost Savings Restructuring Program | Severance and other
Restructuring Reserve [Roll Forward]
Beginning Reserve Balance	0
Charged to Costs and Expenses	8
Payments and Other	(6)
Ending Reserve Balance	2	$ 0
Restructuring charges incurred to date	$ 8