Financial Instruments (Details 3) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Proceeds from Marketable Debt Securities
Proceeds from maturities and sales	$ 560,100,000	$ 78,300,000	$ 1,317,525,000	$ 4,404,707,000
Realized gains	200,000	0	400,000	6,300,000
Realized losses	$ (100,000)	$ 0	$ (200,000)	$ (2,000,000)