Amortized Cost and Fair Value of Investments in Debt Securities by Estimated Average Life (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Distribution of Maturities: Amortized Cost, 1 Year or Less	$ 1,780
Distribution of Maturities: Amortized Cost, 1-5 Years	12,803
Distribution of Maturities: Amortized Cost, 5-10 Years	4,183
Distribution of Maturities: Amortized Cost, After 10 Years	3,604
Distribution of Maturities: Amortized Cost, Total	22,370
Distribution of Maturities: Fair Value, 1 Year or Less	1,862
Distribution of Maturities: Fair Value, 1-5 Years	13,184
Distribution of Maturities: Fair Value, 5-10 Years	4,062
Distribution of Maturities: Fair Value, After 10 Years	3,407
Distribution of Maturities: Fair Value, Total	22,515
Available For Sale Securities Debt Maturities, Yield, One Year Or Less	3.02%	[1]
Available For Sale Securities Debt Maturities, Yield, After One Through Five Years	2.87%	[1]
Available For Sale Securities Debt Maturities, Yield, After Five Through Ten Years	2.26%	[1]
Available For Sale Securities Debt Maturities, Yield, After Ten Years	2.68%	[1]
Available For Sale Securities Debt Maturities, Yield	2.72%	[1]
US Treasury Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	1
Distribution of Maturities: Amortized Cost, 1-5 Years	201
Distribution of Maturities: Amortized Cost, 5-10 Years	591
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	793
Distribution of Maturities: Fair Value, 1 Year or Less	1
Distribution of Maturities: Fair Value, 1-5 Years	208
Distribution of Maturities: Fair Value, 5-10 Years	569
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	778
US Government Agencies Debt Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	63
Distribution of Maturities: Amortized Cost, 1-5 Years	1,391
Distribution of Maturities: Amortized Cost, 5-10 Years	594
Distribution of Maturities: Amortized Cost, After 10 Years	155
Distribution of Maturities: Amortized Cost, Total	2,203
Distribution of Maturities: Fair Value, 1 Year or Less	63
Distribution of Maturities: Fair Value, 1-5 Years	1,439
Distribution of Maturities: Fair Value, 5-10 Years	567
Distribution of Maturities: Fair Value, After 10 Years	153
Distribution of Maturities: Fair Value, Total	2,222
US States and Political Subdivisions Debt Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	90
Distribution of Maturities: Amortized Cost, 1-5 Years	102
Distribution of Maturities: Amortized Cost, 5-10 Years	11
Distribution of Maturities: Amortized Cost, After 10 Years	45
Distribution of Maturities: Amortized Cost, Total	248
Distribution of Maturities: Fair Value, 1 Year or Less	92
Distribution of Maturities: Fair Value, 1-5 Years	108
Distribution of Maturities: Fair Value, 5-10 Years	12
Distribution of Maturities: Fair Value, After 10 Years	44
Distribution of Maturities: Fair Value, Total	256
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Distribution of Maturities: Amortized Cost, 1 Year or Less	1,539
Distribution of Maturities: Amortized Cost, 1-5 Years	10,915
Distribution of Maturities: Amortized Cost, 5-10 Years	2,926
Distribution of Maturities: Amortized Cost, After 10 Years	3,404
Distribution of Maturities: Amortized Cost, Total	18,784
Distribution of Maturities: Fair Value, 1 Year or Less	1,620
Distribution of Maturities: Fair Value, 1-5 Years	11,231
Distribution of Maturities: Fair Value, 5-10 Years	2,852
Distribution of Maturities: Fair Value, After 10 Years	3,210
Distribution of Maturities: Fair Value, Total	18,913
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	0
Distribution of Maturities: Amortized Cost, 1-5 Years	142
Distribution of Maturities: Amortized Cost, 5-10 Years	39
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	181
Distribution of Maturities: Fair Value, 1 Year or Less	0
Distribution of Maturities: Fair Value, 1-5 Years	142
Distribution of Maturities: Fair Value, 5-10 Years	39
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	181
Asset-backed Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	87
Distribution of Maturities: Amortized Cost, 1-5 Years	35
Distribution of Maturities: Amortized Cost, 5-10 Years	2
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	124
Distribution of Maturities: Fair Value, 1 Year or Less	86
Distribution of Maturities: Fair Value, 1-5 Years	37
Distribution of Maturities: Fair Value, 5-10 Years	2
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	125
Other Debt Obligations [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	0
Distribution of Maturities: Amortized Cost, 1-5 Years	17
Distribution of Maturities: Amortized Cost, 5-10 Years	20
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	37
Distribution of Maturities: Fair Value, 1 Year or Less	0
Distribution of Maturities: Fair Value, 1-5 Years	19
Distribution of Maturities: Fair Value, 5-10 Years	21
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	$ 40

[1] Average yields are based on amortized cost and presented on a FTE basis.