Investments (Investment Securities Whose Book Value Exceeded Market Value By More Than 5%) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012 Security
5% To Less Than 16% [Member]
Schedule of Investments [Line Items]
Number of Securities	39
Book Value	$ 1,784
Fair Value	1,615
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 Investments [Line Items]
Number of Securities	19
Book Value	159
Fair Value	124
Percentage Book Value Exceeded Market Value, Minimum	16.00%
Percentage Book Value Exceeded Market Value, Maximum	26.00%
26% To 50% [Member]
Schedule of Investments [Line Items]
Number of Securities	39
Book Value	170
Fair Value	105
Percentage Book Value Exceeded Market Value, Minimum	26.00%
Percentage Book Value Exceeded Market Value, Maximum	50.00%
Greater Than 50% [Member]
Schedule of Investments [Line Items]
Number of Securities	34
Book Value	99
Fair Value	22
Percentage Book Value Exceeded Market Value, Maximum	50.00%
Greater Than 5% [Member]
Schedule of Investments [Line Items]
Number of Securities	131
Book Value	2,212
Fair Value	$ 1,866