Investments (Investment Securities Whose Book Value Exceeded Market Value By More Than 5%) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	218
Book Value	$ 4,087
Fair Value	3,309
5% To Less Than 16% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	56
Book Value	2,341
Fair Value	2,091
Percentage Book Value Exceeded Market Value, Minimum	5.00%
Percentage Book Value Exceeded Market Value, Maximum	16.00%
16% To Less Than 26% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	42
Book Value	1,047
Fair Value	821
Percentage Book Value Exceeded Market Value, Minimum	16.00%
Percentage Book Value Exceeded Market Value, Maximum	26.00%
26% To 50% [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Securities	79
Book Value	532
Fair Value	350
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	41
Book Value	167
Fair Value	$ 47
Percentage Book Value Exceeded Market Value, Minimum	50.00%