3. Fair Value Measurements Amortized Cost and Fair Value of Debt Securities (Details) $ in Millions	Dec. 31, 2016 USD ($)
Fair Value Disclosures [Abstract]
Mature in less than one year	$ 156.1
Mature in one to five years	141.0
Mature in more than five years	51.7
Total Amortized Cost	348.8
Mature in less than one year	156.1
Mature in one to five years	140.7
Mature in more than five years	51.0
Estimated Fair Value	$ 347.8