Amortized Cost and Fair Value of Investments in Debt Securities by Estimated Average Life (Detail) - Jun. 30, 2015 - USD ($) $ in Millions		Total
Distribution of Maturities: Amortized Cost, 1 Year or Less		$ 3,002
Distribution of Maturities: Amortized Cost, 1-5 Years		14,356
Distribution of Maturities: Amortized Cost, 5-10 Years		4,480
Distribution of Maturities: Amortized Cost, After 10 Years		4,302
Distribution of Maturities: Amortized Cost, Total		26,140
Distribution of Maturities: Fair Value, 1 Year or Less		3,159
Distribution of Maturities: Fair Value, 1-5 Years		14,625
Distribution of Maturities: Fair Value, 5-10 Years		4,458
Distribution of Maturities: Fair Value, After 10 Years		4,231
Distribution of Maturities: Fair Value, Total		$ 26,473
Available For Sale Securities Debt Maturities, Yield, One Year Or Less	[1]	2.19%
Available For Sale Securities Debt Maturities, Yield, After One Through Five Years	[1]	2.29%
Available For Sale Securities Debt Maturities, Yield, After Five Through Ten Years	[1]	2.66%
Available For Sale Securities Debt Maturities, Yield, After Ten Years	[1]	2.77%
Available For Sale Securities Debt Maturities, Yield	[1]	2.40%
US Treasury Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less		$ 200
Distribution of Maturities: Amortized Cost, 1-5 Years		1,717
Distribution of Maturities: Amortized Cost, 5-10 Years		988
Distribution of Maturities: Amortized Cost, After 10 Years		0
Distribution of Maturities: Amortized Cost, Total		2,905
Distribution of Maturities: Fair Value, 1 Year or Less		202
Distribution of Maturities: Fair Value, 1-5 Years		1,725
Distribution of Maturities: Fair Value, 5-10 Years		986
Distribution of Maturities: Fair Value, After 10 Years		0
Distribution of Maturities: Fair Value, Total		2,913
US Government Agencies Debt Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less		80
Distribution of Maturities: Amortized Cost, 1-5 Years		209
Distribution of Maturities: Amortized Cost, 5-10 Years		42
Distribution of Maturities: Amortized Cost, After 10 Years		135
Distribution of Maturities: Amortized Cost, Total		466
Distribution of Maturities: Fair Value, 1 Year or Less		80
Distribution of Maturities: Fair Value, 1-5 Years		219
Distribution of Maturities: Fair Value, 5-10 Years		44
Distribution of Maturities: Fair Value, After 10 Years		134
Distribution of Maturities: Fair Value, Total		477
US States and Political Subdivisions Debt Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less		42
Distribution of Maturities: Amortized Cost, 1-5 Years		20
Distribution of Maturities: Amortized Cost, 5-10 Years		101
Distribution of Maturities: Amortized Cost, After 10 Years		15
Distribution of Maturities: Amortized Cost, Total		178
Distribution of Maturities: Fair Value, 1 Year or Less		42
Distribution of Maturities: Fair Value, 1-5 Years		21
Distribution of Maturities: Fair Value, 5-10 Years		105
Distribution of Maturities: Fair Value, After 10 Years		16
Distribution of Maturities: Fair Value, Total		184
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less		2,664
Distribution of Maturities: Amortized Cost, 1-5 Years		12,267
Distribution of Maturities: Amortized Cost, 5-10 Years		3,348
Distribution of Maturities: Amortized Cost, After 10 Years		4,152
Distribution of Maturities: Amortized Cost, Total		22,431
Distribution of Maturities: Fair Value, 1 Year or Less		2,819
Distribution of Maturities: Fair Value, 1-5 Years		12,511
Distribution of Maturities: Fair Value, 5-10 Years		3,322
Distribution of Maturities: Fair Value, After 10 Years		4,081
Distribution of Maturities: Fair Value, Total		22,733
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		110
Distribution of Maturities: Amortized Cost, 5-10 Years		0
Distribution of Maturities: Amortized Cost, After 10 Years		0
Distribution of Maturities: Amortized Cost, Total		110
Distribution of Maturities: Fair Value, 1 Year or Less		0
Distribution of Maturities: Fair Value, 1-5 Years		112
Distribution of Maturities: Fair Value, 5-10 Years		0
Distribution of Maturities: Fair Value, After 10 Years		0
Distribution of Maturities: Fair Value, Total		112
Asset-backed Securities [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less		13
Distribution of Maturities: Amortized Cost, 1-5 Years		1
Distribution of Maturities: Amortized Cost, 5-10 Years		1
Distribution of Maturities: Amortized Cost, After 10 Years		0
Distribution of Maturities: Amortized Cost, Total		15
Distribution of Maturities: Fair Value, 1 Year or Less		13
Distribution of Maturities: Fair Value, 1-5 Years		3
Distribution of Maturities: Fair Value, 5-10 Years		1
Distribution of Maturities: Fair Value, After 10 Years		0
Distribution of Maturities: Fair Value, Total		17
Other Debt Obligations [Member]
Distribution of Maturities: Amortized Cost, 1 Year or Less		3
Distribution of Maturities: Amortized Cost, 1-5 Years		32
Distribution of Maturities: Amortized Cost, 5-10 Years		0
Distribution of Maturities: Amortized Cost, After 10 Years		0
Distribution of Maturities: Amortized Cost, Total		35
Distribution of Maturities: Fair Value, 1 Year or Less		3
Distribution of Maturities: Fair Value, 1-5 Years		34
Distribution of Maturities: Fair Value, 5-10 Years		0
Distribution of Maturities: Fair Value, After 10 Years		0
Distribution of Maturities: Fair Value, Total		$ 37

[1] Weighted average yields are based on amortized cost and presented on an FTE basis.