Fair Value Measurements Variable Interest Entity (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2004
Variable Interest Entity [Line Items]
Type of Entity	bankruptcy-remote, limited liability subsidiary
Date involvement began	2004
Amount of installment note and letter of credit contributed to special purpose entity		$ 25.0
Amount of cash received		22.6
Interest cash payments received, net	immaterial cash payments
Classification of carrying amount of interest	"Other Assets"
Recorded liability for performance obligation	de minimus guarantee liability
Type of financial obligation	make-whole agreement
Cash to be received upon maturity	2.6
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Amount of notes issued by special purpose entity		22.6
Term of notes issued by special purpose entity		15-year
Variable Interest Entity Investment	$ 2.6
Maturity date of notes issued by special purpose entity	2019