Investment Securities - Investment Securities (Detail) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost		$ 59,704	$ 55,432
Available-for-sale securities, total, fair value	[1]	$ 60,396	$ 56,069
Available-for-sale securities, total, weighted average yield		2.19%	2.32%
Available-for-sale securities, total, weighted average maturity in years		4 years 4 months 24 days	4 years 3 months 18 days
Held-to-maturity securities, total, amortized cost	[1]	$ 44,690	$ 44,974
Held-to-maturity securities, total, fair value		$ 45,051	$ 45,140
Held-to-maturity securities, total, weighted average yield		1.86%	1.92%
Held-to-maturity securities, total, weighted average maturity in years		4 years	4 years
Amortized Cost of Investment Securities		$ 104,394	$ 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		$ 374
Available-for-sale securities, maturing after one year through five years, amortized cost		1,488
Available-for-sale securities, maturing after five years through ten years, amortized cost		972
Available-for-sale securities, maturing after ten years, amortized cost		1
Available-for-sale securities, total, amortized cost		2,835	$ 2,622
Available-for-sale securities, maturing in one year or less, fair value		375
Available-for-sale securities, maturing after one year through five years, fair value		1,509
Available-for-sale securities, maturing after five years through ten years, fair value		989
Available-for-sale securities, maturing after ten years, fair value		1
Available-for-sale securities, total, fair value		$ 2,874	2,632
Available-for-sale securities, maturing in one year or less, weighted average yield		2.52%
Available-for-sale securities, maturing in one year or less, weighted average maturity in years		4 months 24 days
Available for sale securities, maturing after one year through five years, weighted average yield		1.42%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		2 years 9 months 18 days
Available-for-sale securities, maturing after five years through ten years, weighted average yield		2.28%
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		4.15%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		11 years 10 months 24 days
Available-for-sale securities, total, weighted average yield		1.86%
Available-for-sale securities, total, weighted average maturity in years		3 years 10 months 24 days
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 1,098
Held to maturity securities, maturing after one year through five years, fair value		1,114
Held-to-maturity securities, maturing after five years through ten years, amortized cost		1,783
Held-to-maturity securities, maturing after five years through ten years, fair value		1,805
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		2,937	2,717
Held-to-maturity securities, total, fair value		$ 2,975	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		2 years 10 months 24 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		2.15%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		7 years
Held-to-maturity securities, maturing after ten years, weighted average yield		1.78%
Held-to-maturity securities, maturing after ten years, weighted average maturity in years		10 years 1 month 6 days
Held-to-maturity securities, total, weighted average yield		1.87%
Held-to-maturity securities, total, weighted average maturity in years		5 years 6 months
Amortized Cost of Investment Securities		$ 5,772	$ 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		$ 836
Available-for-sale securities, maturing after one year through five years, amortized cost		38,148
Available-for-sale securities, maturing after five years through ten years, amortized cost		10,540
Available-for-sale securities, maturing after ten years, amortized cost		558
Available-for-sale securities, total, amortized cost		50,082
Available-for-sale securities, maturing in one year or less, fair value		840
Available-for-sale securities, maturing after one year through five years, fair value		38,531
Available-for-sale securities, maturing after five years through ten years, fair value		10,625
Available-for-sale securities, maturing after ten years, fair value		560
Available-for-sale securities, total, fair value		$ 50,556
Available-for-sale securities, maturing in one year or less, weighted average yield		1.68%
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		1.83%
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		1.43%
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 9 months 18 days
Available-for-sale securities, total, weighted average yield		1.73%
Available-for-sale securities, total, weighted average maturity in years		4 years 4 months 24 days
Held-to-maturity securities, maturing in one year or less, amortized cost		$ 349
Held-to-maturity securities, maturing in one year or less, fair value		350
Held-to-maturity securities, maturing after one year through five years, amortized cost		36,027
Held to maturity securities, maturing after one year through five years, fair value		36,296
Held-to-maturity securities, maturing after five years through ten years, amortized cost		5,161
Held-to-maturity securities, maturing after five years through ten years, fair value		5,206
Held-to-maturity securities, maturing after ten years, amortized cost		168
Held-to-maturity securities, maturing after ten years, fair value		168
Held-to-maturity securities, total, amortized cost		41,705
Held-to-maturity securities, total, fair value		$ 42,020
Held-to-maturity securities, maturing in one year or less, weighted average yield		1.69%
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		1.96%
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		1.21%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		5 years 7 months 6 days
Held-to-maturity securities, maturing after ten years, weighted average yield		1.22%
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		1.86%
Held-to-maturity securities, total, weighted average maturity in years		3 years 10 months 24 days
Amortized Cost of Investment Securities		$ 91,787	$ 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		$ 52
Available-for-sale securities, maturing after one year through five years, amortized cost		199
Available-for-sale securities, maturing after five years through ten years, amortized cost		354
Available-for-sale securities, total, amortized cost		605
Available-for-sale securities, maturing in one year or less, fair value		53
Available-for-sale securities, maturing after one year through five years, fair value		205
Available-for-sale securities, maturing after five years through ten years, fair value		361
Available-for-sale securities, total, fair value		$ 619
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		6 months
Available for sale securities, maturing after one year through five years, weighted average yield		3.00%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		3 years 6 months
Available-for-sale securities, maturing after five years through ten years, weighted average yield		2.16%
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years		6 years 2 months 12 days
Available-for-sale securities, total, weighted average yield		2.26%
Available-for-sale securities, total, weighted average maturity in years		4 years 9 months 18 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		5
Held to maturity securities, maturing after one year through five years, fair value		8
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		4
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		10
Held-to-maturity securities, total, fair value		$ 20
Held-to-maturity securities, maturing in one year or less, weighted average yield		0.82%
Held-to-maturity securities, maturing in one year or less, weighted average maturity in years		2 months 12 days
Held-to-maturity securities, maturing after one year through five years, weighted average yield		0.86%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		2 years 4 months 24 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		0.92%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		5 years 9 months 18 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 10 months 24 days
Held-to-maturity securities, total, weighted average yield		0.89%
Held-to-maturity securities, total, weighted average maturity in years		4 years 8 months 12 days
Amortized Cost of Investment Securities		$ 615	$ 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		$ 1,581
Available-for-sale securities, maturing after one year through five years, amortized cost		2,753
Available-for-sale securities, maturing after five years through ten years, amortized cost		635
Available-for-sale securities, maturing after ten years, amortized cost		152
Available-for-sale securities, total, amortized cost		5,121	$ 5,604
Available-for-sale securities, maturing in one year or less, fair value		1,614
Available-for-sale securities, maturing after one year through five years, fair value		2,891
Available-for-sale securities, maturing after five years through ten years, fair value		639
Available-for-sale securities, maturing after ten years, fair value		158
Available-for-sale securities, total, fair value		$ 5,302	5,868
Available-for-sale securities, maturing in one year or less, weighted average yield		7.01%
Available-for-sale securities, maturing in one year or less, weighted average maturity in years		7 months 6 days
Available for sale securities, maturing after one year through five years, weighted average yield		6.91%
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years		1 year 9 months 18 days
Available-for-sale securities, maturing after five years through ten years, weighted average yield		5.40%
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years		7 years 2 months 12 days
Available-for-sale securities, maturing after ten years, weighted average yield		6.81%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		16 years 7 months 6 days
Available-for-sale securities, total, weighted average yield		6.75%
Available-for-sale securities, total, weighted average maturity in years		2 years 6 months
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		1
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		8	9
Held-to-maturity securities, total, fair value		$ 8	9
Held-to-maturity securities, maturing in one year or less, weighted average yield		9.50%
Held-to-maturity securities, maturing in one year or less, weighted average maturity in years		2 months 12 days
Held-to-maturity securities, maturing after one year through five years, weighted average yield		7.93%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		2 years 8 months 12 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		7.78%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		8 years
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 7 months 6 days
Held-to-maturity securities, total, weighted average yield		3.72%
Held-to-maturity securities, total, weighted average maturity in years		9 years
Amortized Cost of Investment Securities		$ 5,129	$ 5,613
Amortized Cost of Investment Securities, Percentage		4.90%	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		$ 677
Available-for-sale securities, total, amortized cost		677
Available-for-sale securities, maturing after ten years, fair value		616
Available-for-sale securities, total, fair value		$ 616
Available-for-sale securities, maturing after ten years, weighted average yield		2.55%
Available-for-sale securities, maturing after ten years, weighted average maturity in years		17 years 9 months 18 days
Available-for-sale securities, total, weighted average yield		2.55%
Available-for-sale securities, total, weighted average maturity in years		17 years 9 months 18 days
Held-to-maturity securities, maturing in one year or less, amortized cost		$ 1
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		8
Held to maturity securities, maturing after one year through five years, fair value		8
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		19
Held-to-maturity securities, total, amortized cost		30
Held-to-maturity securities, total, fair value		$ 28
Held-to-maturity securities, maturing in one year or less, weighted average yield		1.39%
Held-to-maturity securities, maturing in one year or less, weighted average maturity in years		9 months 18 days
Held-to-maturity securities, maturing after one year through five years, weighted average yield		1.50%
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years		1 year 7 months 6 days
Held-to-maturity securities, maturing after five years through ten years, weighted average yield		1.05%
Held-to-maturity securities, maturing after five years through ten years, weighted average maturity in years		5 years 1 month 6 days
Held-to-maturity securities, total, weighted average yield		1.18%
Held-to-maturity securities, total, weighted average maturity in years		4 years
Amortized Cost of Investment Securities		$ 1,091	$ 1,171
Amortized Cost of Investment Securities, Percentage		1.10%	1.20%
Other Investments Including Perpetual Preferred Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost		$ 384
Available-for-sale securities, total, fair value		$ 429
Available-for-sale securities, total, weighted average yield		2.41%
Available-for-sale securities, total, weighted average maturity in years		11 years 7 months 6 days

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