Short-term Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 15
Period for term note facility (in years)		1 year
Total borrowings	$ 5	$ 10
Description of variable rate basis	LIBOR plus 2.5%
LIBOR [Member]
Debt Instrument [Line Items]
Effective interest rate (in hundredths)		0.50%
Federal [Member]
Debt Instrument [Line Items]
Effective interest rate (in hundredths)		2.50%