Short-Term Borrowings and Credit Arrangements Unsecured Revolving Line of Credit (Details) (Unsecured Revolving Line Of Credit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 numberofbanks	Dec. 31, 2012
Line of Credit Facility [Line Items]
Current borrowing capacity	$ 300
Maximum borrowing capacity	350
Number of institutions participating in the credit facility	8
Maximum number of institutions participating in the credit faciltiy pertaining to maximum contributory percentage	1
Commitment fees	0.5	0.5
Letters of credit outstanding, amount	$ 0
Maximum [Member]
Line of Credit Facility [Line Items]
Maximum percentage of total availability provided by a single lender	16.00%
Maximum ratio of indebtedness to net capital threshold percentage	65.00%
Eurodollar [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.88%
Eurodollar [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
Base Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Base Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.75%