Investments (Investment Securities Whose Book Value Exceeded Market Value By More Than 5%) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	215
Book Value	$ 4,255
Fair Value	3,426
5% To 15% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	52
Book Value	2,358
Fair Value	2,136
Percentage Book Value Exceeded Market Value, Minimum	5.00%
Percentage Book Value Exceeded Market Value, Maximum	15.00%
16% To 25% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	51
Book Value	1,096
Fair Value	860
Percentage Book Value Exceeded Market Value, Minimum	16.00%
Percentage Book Value Exceeded Market Value, Maximum	25.00%
26% To 50% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	79
Book Value	556
Fair Value	370
Percentage Book Value Exceeded Market Value, Minimum	26.00%
Percentage Book Value Exceeded Market Value, Maximum	50.00%
Greater Than 50% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	33
Book Value	245
Fair Value	$ 60
Percentage Book Value Exceeded Market Value, Minimum	50.00%