Financial Instruments (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Proceeds from Marketable Debt Securities
Proceeds from maturities and sales	$ 757,512,000	$ 4,329,506,000
Realized gains	200,000	6,300,000
Realized losses	$ (100,000)	$ (2,000,000)