Fair Value of Financial Instruments (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Investments in time and call deposits
Unrealized gains (losses) on available-for-sale securities	$ 0
Minimum
Investments in time and call deposits
Maturity of time deposits	1 month
Period of ability to redeem invested amounts on call deposits	31 days
Maximum
Investments in time and call deposits
Maturity of time deposits	12 months
Period of ability to redeem invested amounts on call deposits	95 days