Capital Stock (Stock Repurchases Pursuant To Board Of Director Authorizations) (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchased	8.7	9.7	27.8
Stock repurchase program remaining authorization	10.6
1997 Authorization
Equity, Class of Treasury Stock [Line Items]
Stock repurchased	0.0	0.0	0.9
Stock repurchase program remaining authorization	0.0
2007 Authorization
Equity, Class of Treasury Stock [Line Items]
Stock repurchased	0.0	0.0	0.9
Stock repurchase program remaining authorization	0.0
2014 Authorization
Equity, Class of Treasury Stock [Line Items]
Stock repurchased	0.0	0.0	20.0
Stock repurchase program remaining authorization	0.0
2015 Authorization
Equity, Class of Treasury Stock [Line Items]
Stock repurchased	0.0	9.0	6.0
Stock repurchase program remaining authorization	0.0
2016 Authorization
Equity, Class of Treasury Stock [Line Items]
Stock repurchased	8.7	0.7	0.0
Stock repurchase program remaining authorization	10.6