Investments (Investment Securities Whose Book Value Exceeded Market Value by More than 5%) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Number of Securities	254
Book Value	$ 3,108
Fair Value	2,574
5% to 15% [Member]
Number of Securities	96
Book Value	2,124
Fair Value	1,959
Percentage Book Value Exceeded Market Value, Minimum	5.00%
Percentage Book Value Exceeded Market Value, Maximum	15.00%
16% to 25% [Member]
Number of Securities	50
Book Value	444
Fair Value	357
Percentage Book Value Exceeded Market Value, Minimum	16.00%
Percentage Book Value Exceeded Market Value, Maximum	25.00%
26% to 50% [Member]
Number of Securities	66
Book Value	292
Fair Value	187
Percentage Book Value Exceeded Market Value, Minimum	26.00%
Percentage Book Value Exceeded Market Value, Maximum	50.00%
Greater than 50% [Member]
Number of Securities	42
Book Value	248
Fair Value	$ 71
Percentage Book Value Exceeded Market Value, Minimum	50.00%