Amortized Cost and Fair Value of Investments in Debt Securities by Estimated Average Life (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014
Distribution of Maturities: Amortized Cost, 1 Year or Less	$ 2,148
Distribution of Maturities: Amortized Cost, 1-5 Years	8,079
Distribution of Maturities: Amortized Cost, 5-10 Years	8,735
Distribution of Maturities: Amortized Cost, After 10 Years	3,753
Distribution of Maturities: Amortized Cost, Total	22,715
Distribution of Maturities: Fair Value, 1 Year or Less	2,267
Distribution of Maturities: Fair Value, 1-5 Years	8,295
Distribution of Maturities: Fair Value, 5-10 Years	8,837
Distribution of Maturities: Fair Value, After 10 Years	3,684
Distribution of Maturities: Fair Value, Total	23,083
Available For Sale Securities Debt Maturities, Yield, One Year Or Less	2.71%	[1]
Available For Sale Securities Debt Maturities, Yield, After One Through Five Years	2.44%	[1]
Available For Sale Securities Debt Maturities, Yield, After Five Through Ten Years	2.86%	[1]
Available For Sale Securities Debt Maturities, Yield, After Ten Years	2.92%	[1]
Available For Sale Securities Debt Maturities, Yield	2.71%	[1]
US Treasury Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	0
Distribution of Maturities: Amortized Cost, 1-5 Years	892
Distribution of Maturities: Amortized Cost, 5-10 Years	689
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	1,581
Distribution of Maturities: Fair Value, 1 Year or Less	0
Distribution of Maturities: Fair Value, 1-5 Years	900
Distribution of Maturities: Fair Value, 5-10 Years	674
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	1,574
US Government Agencies Debt Securities
Distribution of Maturities: Amortized Cost, 1 Year or Less	71
Distribution of Maturities: Amortized Cost, 1-5 Years	247
Distribution of Maturities: Amortized Cost, 5-10 Years	543
Distribution of Maturities: Amortized Cost, After 10 Years	144
Distribution of Maturities: Amortized Cost, Total	1,005
Distribution of Maturities: Fair Value, 1 Year or Less	71
Distribution of Maturities: Fair Value, 1-5 Years	259
Distribution of Maturities: Fair Value, 5-10 Years	518
Distribution of Maturities: Fair Value, After 10 Years	142
Distribution of Maturities: Fair Value, Total	990
US States and Political Subdivisions Debt Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	65
Distribution of Maturities: Amortized Cost, 1-5 Years	53
Distribution of Maturities: Amortized Cost, 5-10 Years	102
Distribution of Maturities: Amortized Cost, After 10 Years	23
Distribution of Maturities: Amortized Cost, Total	243
Distribution of Maturities: Fair Value, 1 Year or Less	66
Distribution of Maturities: Fair Value, 1-5 Years	56
Distribution of Maturities: Fair Value, 5-10 Years	104
Distribution of Maturities: Fair Value, After 10 Years	25
Distribution of Maturities: Fair Value, Total	251
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Distribution of Maturities: Amortized Cost, 1 Year or Less	1,995
Distribution of Maturities: Amortized Cost, 1-5 Years	6,727
Distribution of Maturities: Amortized Cost, 5-10 Years	7,384
Distribution of Maturities: Amortized Cost, After 10 Years	3,586
Distribution of Maturities: Amortized Cost, Total	19,692
Distribution of Maturities: Fair Value, 1 Year or Less	2,114
Distribution of Maturities: Fair Value, 1-5 Years	6,912
Distribution of Maturities: Fair Value, 5-10 Years	7,522
Distribution of Maturities: Fair Value, After 10 Years	3,517
Distribution of Maturities: Fair Value, Total	20,065
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	136
Distribution of Maturities: Amortized Cost, 5-10 Years	0
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	136
Distribution of Maturities: Fair Value, 1 Year or Less	0
Distribution of Maturities: Fair Value, 1-5 Years	140
Distribution of Maturities: Fair Value, 5-10 Years	0
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	140
Asset-backed Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	15
Distribution of Maturities: Amortized Cost, 1-5 Years	4
Distribution of Maturities: Amortized Cost, 5-10 Years	1
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	20
Distribution of Maturities: Fair Value, 1 Year or Less	14
Distribution of Maturities: Fair Value, 1-5 Years	6
Distribution of Maturities: Fair Value, 5-10 Years	2
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	22
Other Debt Obligations [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less	2
Distribution of Maturities: Amortized Cost, 1-5 Years	20
Distribution of Maturities: Amortized Cost, 5-10 Years	16
Distribution of Maturities: Amortized Cost, After 10 Years	0
Distribution of Maturities: Amortized Cost, Total	38
Distribution of Maturities: Fair Value, 1 Year or Less	2
Distribution of Maturities: Fair Value, 1-5 Years	22
Distribution of Maturities: Fair Value, 5-10 Years	17
Distribution of Maturities: Fair Value, After 10 Years	0
Distribution of Maturities: Fair Value, Total	$ 41

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