Fair Value Fair Value (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Fair Value, Inputs, Level 1 [Member]
Fair Value Transfers Between Level 1, Level 2 and Level 3 [Line Items]
Transfers into Level 2	$ 0	$ 0
Transfers into Level 3	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value Transfers Between Level 1, Level 2 and Level 3 [Line Items]
Transfers into Level 1	0	0
Transfers into Level 3	0	27
Fair Value, Inputs, Level 3 [Member]
Fair Value Transfers Between Level 1, Level 2 and Level 3 [Line Items]
Transfers into Level 1	0	0
Transfers into Level 2	$ 2	$ 2