Stock-Based Compensation Plans (Employee Stock Purchase Plan) (Details) - $ / shares	12 Months Ended			84 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, granted (in shares)	1,049,000	1,613,000	1,295,000
Wtd. Avg Grant Date Fair Value, Granted (in dollars per share)	$ 4	$ 5	$ 4
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, granted (in shares)	173,013	177,846	175,479	1,145,856
Wtd. Avg Grant Date Fair Value, Granted (in dollars per share)				$ 21.40