Amortized Cost and Fair Value of Investments in Debt Securities by Estimated Average Life (Detail) (USD $) In Millions	Jun. 30, 2011
Distribution of Maturities: Amortized Cost, 1 Year or Less	$ 1,554
Distribution of Maturities: Amortized Cost, 1-5 Years	14,759
Distribution of Maturities: Amortized Cost, 5-10 Years	2,096
Distribution of Maturities: Amortized Cost, After 10 Years	5,477
Distribution of Maturities: Amortized Cost, Total	23,886
Distribution of Maturities: Fair Value, 1 Year or Less	1,583
Distribution of Maturities: Fair Value, 1-5 Years	15,174
Distribution of Maturities: Fair Value, 5-10 Years	2,143
Distribution of Maturities: Fair Value, After 10 Years	5,568
Distribution of Maturities: Fair Value, Total	24,468
US Treasury Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	8
Distribution of Maturities: Amortized Cost, 1-5 Years	214
Distribution of Maturities: Amortized Cost, 5-10 Years	508
Distribution of Maturities: Amortized Cost, Total	730
Distribution of Maturities: Fair Value, 1 Year or Less	8
Distribution of Maturities: Fair Value, 1-5 Years	219
Distribution of Maturities: Fair Value, 5-10 Years	499
Distribution of Maturities: Fair Value, Total	726
US Government Agencies Debt Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	60
Distribution of Maturities: Amortized Cost, 1-5 Years	2,010
Distribution of Maturities: Amortized Cost, 5-10 Years	414
Distribution of Maturities: Amortized Cost, After 10 Years	35
Distribution of Maturities: Amortized Cost, Total	2,519
Distribution of Maturities: Fair Value, 1 Year or Less	60
Distribution of Maturities: Fair Value, 1-5 Years	2,044
Distribution of Maturities: Fair Value, 5-10 Years	427
Distribution of Maturities: Fair Value, After 10 Years	35
Distribution of Maturities: Fair Value, Total	2,566
US States and Political Subdivisions Debt Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	131
Distribution of Maturities: Amortized Cost, 1-5 Years	255
Distribution of Maturities: Amortized Cost, 5-10 Years	44
Distribution of Maturities: Amortized Cost, After 10 Years	69
Distribution of Maturities: Amortized Cost, Total	499
Distribution of Maturities: Fair Value, 1 Year or Less	135
Distribution of Maturities: Fair Value, 1-5 Years	269
Distribution of Maturities: Fair Value, 5-10 Years	45
Distribution of Maturities: Fair Value, After 10 Years	67
Distribution of Maturities: Fair Value, Total	516
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Distribution of Maturities: Amortized Cost, 1 Year or Less	778
Distribution of Maturities: Amortized Cost, 1-5 Years	11,566
Distribution of Maturities: Amortized Cost, 5-10 Years	1,105
Distribution of Maturities: Amortized Cost, After 10 Years	5,348
Distribution of Maturities: Amortized Cost, Total	18,797
Distribution of Maturities: Fair Value, 1 Year or Less	797
Distribution of Maturities: Fair Value, 1-5 Years	11,947
Distribution of Maturities: Fair Value, 5-10 Years	1,146
Distribution of Maturities: Fair Value, After 10 Years	5,441
Distribution of Maturities: Fair Value, Total	19,331
Mortgage-backed Securities, Issued by Private Enterprises
Distribution of Maturities: Amortized Cost, 1 Year or Less	33
Distribution of Maturities: Amortized Cost, 1-5 Years	300
Distribution of Maturities: Amortized Cost, 5-10 Years	2
Distribution of Maturities: Amortized Cost, Total	335
Distribution of Maturities: Fair Value, 1 Year or Less	30
Distribution of Maturities: Fair Value, 1-5 Years	279
Distribution of Maturities: Fair Value, 5-10 Years	2
Distribution of Maturities: Fair Value, Total	311
Collateralized Debt Obligations
Distribution of Maturities: Amortized Cost, 1 Year or Less	150
Distribution of Maturities: Amortized Cost, 1-5 Years	187
Distribution of Maturities: Amortized Cost, Total	337
Distribution of Maturities: Fair Value, 1 Year or Less	150
Distribution of Maturities: Fair Value, 1-5 Years	187
Distribution of Maturities: Fair Value, Total	337
Asset-backed Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	386
Distribution of Maturities: Amortized Cost, 1-5 Years	223
Distribution of Maturities: Amortized Cost, 5-10 Years	6
Distribution of Maturities: Amortized Cost, Total	615
Distribution of Maturities: Fair Value, 1 Year or Less	395
Distribution of Maturities: Fair Value, 1-5 Years	225
Distribution of Maturities: Fair Value, 5-10 Years	5
Distribution of Maturities: Fair Value, Total	625
Corporate And Other Debt Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	8
Distribution of Maturities: Amortized Cost, 1-5 Years	4
Distribution of Maturities: Amortized Cost, 5-10 Years	17
Distribution of Maturities: Amortized Cost, After 10 Years	25
Distribution of Maturities: Amortized Cost, Total	54
Distribution of Maturities: Fair Value, 1 Year or Less	8
Distribution of Maturities: Fair Value, 1-5 Years	4
Distribution of Maturities: Fair Value, 5-10 Years	19
Distribution of Maturities: Fair Value, After 10 Years	25
Distribution of Maturities: Fair Value, Total	$ 56