Investment Securities - Investment Securities (Detail) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost		$ 56,589	$ 55,432
Available-for-sale securities, total, fair value	[1]	$ 57,078	$ 56,069
Available-for-sale securities, total, weighted average yield		2.23%	2.32%
Available-for-sale securities, total, weighted average maturity in years		4 years 8 months 12 days	4 years 3 months 18 days
Held-to-maturity securities, total, amortized cost	[1]	$ 46,233	$ 44,974
Held-to-maturity securities, total, fair value		$ 46,364	$ 45,140
Held-to-maturity securities, total, weighted average yield		1.85%	1.92%
Held-to-maturity securities, total, weighted average maturity in years		4 years 3 months 18 days	4 years
Amortized Cost of Investment Securities		$ 102,822	$ 100,406
Amortized Cost of Investment Securities, Percentage		100.00%	100.00%
U.S. Treasury and Agencies [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 120
Available-for-sale securities, maturing after one year through five years, amortized cost		1,785
Available-for-sale securities, maturing after five years through ten years, amortized cost		846
Available-for-sale securities, maturing after ten years, amortized cost		1
Available-for-sale securities, total, amortized cost		2,752	$ 2,622
Available-for-sale securities, maturing in one year or less, fair value		121
Available-for-sale securities, maturing after one year through five years, fair value		1,795
Available-for-sale securities, maturing after five years through ten years, fair value		847
Available-for-sale securities, maturing after ten years, fair value		1
Available-for-sale securities, total, fair value		$ 2,764	2,632
Available-for-sale securities, maturing in one year or less, weighted average yield		1.94%
Available-for-sale securities, maturing in one year or less, weighted average maturity in years		2 months 12 days
Available for sale securities, maturing after one year through five years, weighted average yield		1.59%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		3 years 2 months 12 days
Available-for-sale securities, maturing after five years through ten years, weighted average yield		2.35%
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years		7 years
Available-for-sale securities, maturing after ten years, weighted average yield		4.15%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		12 years 2 months 12 days
Available-for-sale securities, total, weighted average yield		1.84%
Available-for-sale securities, total, weighted average maturity in years		4 years 2 months 12 days
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 1,097
Held to maturity securities, maturing after one year through five years, fair value		1,109
Held-to-maturity securities, maturing after five years through ten years, amortized cost		1,700
Held-to-maturity securities, maturing after five years through ten years, fair value		1,688
Held-to-maturity securities, maturing after ten years, amortized cost		56
Held-to-maturity securities, maturing after ten years, fair value		56
Held-to-maturity securities, total, amortized cost		2,853	2,717
Held-to-maturity securities, total, fair value		$ 2,853	2,714
Held-to-maturity securities, maturing after one year through five years, weighted average yield		1.42%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		3 years 2 months 12 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		2.16%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		7 years 2 months 12 days
Held-to-maturity securities, maturing after ten years, weighted average yield		1.77%
Held-to-maturity securities, maturing after ten years, weighted average maturity in years		10 years 3 months 18 days
Held-to-maturity securities, total, weighted average yield		1.87%
Held-to-maturity securities, total, weighted average maturity in years		5 years 8 months 12 days
Amortized Cost of Investment Securities		$ 5,605	$ 5,339
Amortized Cost of Investment Securities, Percentage		5.50%	5.30%
Mortgage-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 438
Available-for-sale securities, maturing after one year through five years, amortized cost		30,054
Available-for-sale securities, maturing after five years through ten years, amortized cost		15,699
Available-for-sale securities, maturing after ten years, amortized cost		867
Available-for-sale securities, total, amortized cost		47,058
Available-for-sale securities, maturing in one year or less, fair value		440
Available-for-sale securities, maturing after one year through five years, fair value		30,255
Available-for-sale securities, maturing after five years through ten years, fair value		15,771
Available-for-sale securities, maturing after ten years, fair value		871
Available-for-sale securities, total, fair value		$ 47,337
Available-for-sale securities, maturing in one year or less, weighted average yield		1.51%
Available-for-sale securities, maturing in one year or less, weighted average maturity in years		8 months 12 days
Available for sale securities, maturing after one year through five years, weighted average yield		1.95%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		4 years
Available-for-sale securities, maturing after five years through ten years, weighted average yield		1.49%
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years		5 years 8 months 12 days
Available-for-sale securities, maturing after ten years, weighted average yield		1.25%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		12 years 2 months 12 days
Available-for-sale securities, total, weighted average yield		1.78%
Available-for-sale securities, total, weighted average maturity in years		4 years 8 months 12 days
Held-to-maturity securities, maturing in one year or less, amortized cost		$ 165
Held-to-maturity securities, maturing in one year or less, fair value		165
Held-to-maturity securities, maturing after one year through five years, amortized cost		31,421
Held to maturity securities, maturing after one year through five years, fair value		31,486
Held-to-maturity securities, maturing after five years through ten years, amortized cost		11,503
Held-to-maturity securities, maturing after five years through ten years, fair value		11,559
Held-to-maturity securities, maturing after ten years, amortized cost		240
Held-to-maturity securities, maturing after ten years, fair value		242
Held-to-maturity securities, total, amortized cost		43,329
Held-to-maturity securities, total, fair value		$ 43,452
Held-to-maturity securities, maturing in one year or less, weighted average yield		1.75%
Held-to-maturity securities, maturing in one year or less, weighted average maturity in years		8 months 12 days
Held-to-maturity securities, maturing after one year through five years, weighted average yield		2.03%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		3 years 8 months 12 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		1.36%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		5 years 6 months
Held-to-maturity securities, maturing after ten years, weighted average yield		1.23%
Held-to-maturity securities, maturing after ten years, weighted average maturity in years		11 years 10 months 24 days
Held-to-maturity securities, total, weighted average yield		1.84%
Held-to-maturity securities, total, weighted average maturity in years		4 years 2 months 12 days
Amortized Cost of Investment Securities		$ 90,387	$ 87,645
Amortized Cost of Investment Securities, Percentage		87.90%	87.30%
Asset-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 53
Available-for-sale securities, maturing after one year through five years, amortized cost		206
Available-for-sale securities, maturing after five years through ten years, amortized cost		355
Available-for-sale securities, total, amortized cost		614
Available-for-sale securities, maturing in one year or less, fair value		56
Available-for-sale securities, maturing after one year through five years, fair value		212
Available-for-sale securities, maturing after five years through ten years, fair value		361
Available-for-sale securities, total, fair value		$ 629
Available-for-sale securities, maturing in one year or less, weighted average yield		0.18%
Available-for-sale securities, maturing in one year or less, weighted average maturity in years		8 months 12 days
Available for sale securities, maturing after one year through five years, weighted average yield		2.00%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		3 years 7 months 6 days
Available-for-sale securities, maturing after five years through ten years, weighted average yield		1.49%
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years		6 years 3 months 18 days
Available-for-sale securities, total, weighted average yield		1.55%
Available-for-sale securities, total, weighted average maturity in years		4 years 10 months 24 days
Held-to-maturity securities, maturing in one year or less, fair value		$ 1
Held-to-maturity securities, maturing after one year through five years, amortized cost		7
Held to maturity securities, maturing after one year through five years, fair value		9
Held-to-maturity securities, maturing after five years through ten years, amortized cost		4
Held-to-maturity securities, maturing after five years through ten years, fair value		5
Held-to-maturity securities, maturing after ten years, amortized cost		1
Held-to-maturity securities, maturing after ten years, fair value		7
Held-to-maturity securities, total, amortized cost		12
Held-to-maturity securities, total, fair value		$ 22
Held-to-maturity securities, maturing in one year or less, weighted average yield		0.81%
Held-to-maturity securities, maturing in one year or less, weighted average maturity in years		1 month 6 days
Held-to-maturity securities, maturing after one year through five years, weighted average yield		0.84%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		3 years
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		0.91%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		6 years 2 months 12 days
Held-to-maturity securities, maturing after ten years, weighted average yield		0.95%
Held-to-maturity securities, maturing after ten years, weighted average maturity in years		11 years 3 months 18 days
Held-to-maturity securities, total, weighted average yield		0.87%
Held-to-maturity securities, total, weighted average maturity in years		4 years 9 months 18 days
Amortized Cost of Investment Securities		$ 626	$ 638
Amortized Cost of Investment Securities, Percentage		0.60%	0.60%
Obligations of State and Political Subdivisions [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 1,244
Available-for-sale securities, maturing after one year through five years, amortized cost		3,412
Available-for-sale securities, maturing after five years through ten years, amortized cost		366
Available-for-sale securities, maturing after ten years, amortized cost		158
Available-for-sale securities, total, amortized cost		5,180	$ 5,604
Available-for-sale securities, maturing in one year or less, fair value		1,267
Available-for-sale securities, maturing after one year through five years, fair value		3,581
Available-for-sale securities, maturing after five years through ten years, fair value		365
Available-for-sale securities, maturing after ten years, fair value		161
Available-for-sale securities, total, fair value		$ 5,374	5,868
Available-for-sale securities, maturing in one year or less, weighted average yield		6.75%
Available-for-sale securities, maturing in one year or less, weighted average maturity in years		6 months
Available for sale securities, maturing after one year through five years, weighted average yield		6.60%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		1 year 10 months 24 days
Available-for-sale securities, maturing after five years through ten years, weighted average yield		4.90%
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years		6 years 10 months 24 days
Available-for-sale securities, maturing after ten years, weighted average yield		6.49%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		18 years
Available-for-sale securities, total, weighted average yield		6.51%
Available-for-sale securities, total, weighted average maturity in years		2 years 4 months 24 days
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 1
Held to maturity securities, maturing after one year through five years, fair value		1
Held-to-maturity securities, maturing after five years through ten years, amortized cost		2
Held-to-maturity securities, maturing after five years through ten years, fair value		2
Held-to-maturity securities, maturing after ten years, amortized cost		6
Held-to-maturity securities, maturing after ten years, fair value		5
Held-to-maturity securities, total, amortized cost		9	9
Held-to-maturity securities, total, fair value		$ 8	9
Held-to-maturity securities, maturing in one year or less, weighted average yield		9.47%
Held-to-maturity securities, maturing in one year or less, weighted average maturity in years		4 months 24 days
Held-to-maturity securities, maturing after one year through five years, weighted average yield		7.89%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		2 years 10 months 24 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		7.76%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		8 years 3 months 18 days
Held-to-maturity securities, maturing after ten years, weighted average yield		1.73%
Held-to-maturity securities, maturing after ten years, weighted average maturity in years		10 years 9 months 18 days
Held-to-maturity securities, total, weighted average yield		3.72%
Held-to-maturity securities, total, weighted average maturity in years		9 years 2 months 12 days
Amortized Cost of Investment Securities		$ 5,189	$ 5,613
Amortized Cost of Investment Securities, Percentage		5.00%	5.60%
Other Debt Securities and Obligations of Foreign Governments [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing after ten years, amortized cost		$ 691
Available-for-sale securities, total, amortized cost		691
Available-for-sale securities, maturing after ten years, fair value		632
Available-for-sale securities, total, fair value		$ 632
Available-for-sale securities, maturing after ten years, weighted average yield		2.49%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		18 years
Available-for-sale securities, total, weighted average yield		2.49%
Available-for-sale securities, total, weighted average maturity in years		18 years
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 9
Held to maturity securities, maturing after one year through five years, fair value		9
Held-to-maturity securities, maturing after five years through ten years, amortized cost		21
Held-to-maturity securities, maturing after five years through ten years, fair value		20
Held-to-maturity securities, total, amortized cost		30
Held-to-maturity securities, total, fair value		$ 29
Held-to-maturity securities, maturing after one year through five years, weighted average yield		1.49%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		1 year 8 months 12 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		1.02%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		5 years 3 months 18 days
Held-to-maturity securities, total, weighted average yield		1.16%
Held-to-maturity securities, total, weighted average maturity in years		4 years 3 months 18 days
Amortized Cost of Investment Securities		$ 1,015	$ 1,171
Amortized Cost of Investment Securities, Percentage		1.00%	1.20%
Other Investments Including Perpetual Preferred Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost		$ 294
Available-for-sale securities, total, fair value		$ 342
Available-for-sale securities, total, weighted average yield		3.15%
Available-for-sale securities, total, weighted average maturity in years		15 years 2 months 12 days

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.