Investment Securities - Investment Securities (Detail) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2016	Dec. 31, 2015
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost		$ 65,496	$ 61,817
Available-for-sale securities, total, weighted-average yield		2.14%	2.21%
Available-for-sale securities, total, fair value	[1]	$ 66,490	$ 61,997
Held-to-maturity securities, total, amortized cost		$ 42,030	$ 43,590
Available-for-sale securities, total, weighted-average maturity in years		3 years 10 months 24 days	4 years 8 months 12 days
Held-to-maturity securities, total, fair value		$ 42,628	$ 43,493
Held-to-maturity securities, total, weighted-average maturity in years		3 years 7 months 6 days	4 years 2 months 12 days
Held-to-maturity securities, total, weighted-average yield		1.92%	1.92%
Amortized Cost of Investment Securities		$ 107,526	$ 105,407
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		$ 1,933
Available-for-sale securities, maturing after one year through five years, amortized cost		5,549
Available-for-sale securities, maturing after five years through ten years, amortized cost		3,912
Available-for-sale securities, maturing after ten years, amortized cost		1
Available-for-sale securities, total, amortized cost		$ 11,395	$ 4,611
Available-for-sale securities, maturing in one year or less, weighted-average yield		1.00%
Available-for-sale securities, maturing in one year or less, fair value		$ 1,936
Available for sale securities, maturing after one year through five years, weighted-average yield		1.16%
Available-for-sale securities, maturing after one year through five years, fair value		$ 5,615
Available-for-sale securities, maturing after five years through ten years, weighted-average yield		1.93%
Available-for-sale securities, maturing after five years through ten years, fair value		$ 4,060
Available-for-sale securities, maturing after ten years, weighted-average yield		4.15%
Available-for-sale securities, maturing after ten years, fair value		$ 1
Available-for-sale securities, total, weighted-average yield		1.40%
Available-for-sale securities, total, fair value		$ 11,612	4,596
Held-to-maturity securities, maturing in one year or less, amortized cost		$ 100
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years		7 months 6 days
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 998
Available-for-sale 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, amortized cost		$ 2,818
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years		6 years 4 months 24 days
Available-for-sale securities, maturing after ten years, weighted -average maturity in years		11 years 2 months 12 days
Held-to-maturity securities, total, amortized cost		$ 3,916	2,925
Available-for-sale securities, total, weighted-average maturity in years		3 years 8 months 12 days
Held-to-maturity securities, maturing in one year or less, fair value		$ 100
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, fair value		$ 1,019
Held-to-maturity securities, maturing after one year through five years, weighted-average maturity in years		2 years 3 months 18 days
Held-to-maturity securities, maturing after five years through ten years, fair value		$ 2,910
Held-to-maturity securities, maturing after five years through ten years, weighted-average maturity in years		6 years 9 months 18 days
Held-to-maturity securities, total, fair value		$ 4,029	2,919
Held-to-maturity securities, total, weighted-average maturity in years		5 years 6 months
Held-to-maturity securities, maturing in one year or less, weighted-average yield		0.91%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield		1.47%
Held-to-maturity securities, maturing after five years through ten years, weighted-average yield		1.95%
Held-to-maturity securities, total, weighted-average yield		1.80%
Amortized Cost of Investment Securities		$ 15,311	$ 7,536
Amortized Cost of Investment Securities, Percentage		14.20%	7.20%
Mortgage-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 921
Available-for-sale securities, maturing after one year through five years, amortized cost		44,355
Available-for-sale securities, maturing after five years through ten years, amortized cost		2,120
Available-for-sale securities, maturing after ten years, amortized cost		187
Available-for-sale securities, total, amortized cost		$ 47,583
Available-for-sale securities, maturing in one year or less, weighted-average yield		1.97%
Available-for-sale securities, maturing in one year or less, fair value		$ 926
Available for sale securities, maturing after one year through five years, weighted-average yield		1.82%
Available-for-sale securities, maturing after one year through five years, fair value		$ 44,896
Available-for-sale securities, maturing after five years through ten years, weighted-average yield		2.00%
Available-for-sale securities, maturing after five years through ten years, fair value		$ 2,155
Available-for-sale securities, maturing after ten years, weighted-average yield		1.55%
Available-for-sale securities, maturing after ten years, fair value		$ 186
Available-for-sale securities, total, weighted-average yield		1.83%
Available-for-sale securities, total, fair value		$ 48,163
Held-to-maturity securities, maturing in one year or less, amortized cost		$ 626
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years		7 months 6 days
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 36,515
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years		3 years 9 months 18 days
Held-to-maturity securities, maturing after five years through ten years, amortized cost		$ 899
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years		6 years 3 months 18 days
Held-to-maturity securities, maturing after ten years, amortized cost		$ 31
Available-for-sale securities, maturing after ten years, weighted -average maturity in years		12 years 3 months 18 days
Held-to-maturity securities, total, amortized cost		$ 38,071
Available-for-sale securities, total, weighted-average maturity in years		3 years 9 months 18 days
Held-to-maturity securities, maturing in one year or less, fair value		$ 629
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, fair value		$ 36,977
Held-to-maturity securities, maturing after one year through five years, weighted-average maturity in years		3 years 4 months 24 days
Held-to-maturity securities, maturing after five years through ten years, fair value		$ 911
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, fair value		$ 31
Held-to-maturity securities, maturing after ten years, weighted-average maturity in years		11 years 7 months 6 days
Held-to-maturity securities, total, fair value		$ 38,548
Held-to-maturity securities, total, weighted-average maturity in years		3 years 4 months 24 days
Held-to-maturity securities, maturing in one year or less, weighted-average yield		2.17%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield		1.93%
Held-to-maturity securities, maturing after five years through ten years, weighted-average yield		1.55%
Held-to-maturity securities, maturing after ten years, weighted-average yield		1.31%
Held-to-maturity securities, total, weighted-average yield		1.93%
Amortized Cost of Investment Securities		$ 85,654	$ 91,265
Amortized Cost of Investment Securities, Percentage		79.70%	86.60%
Asset-Backed Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost		$ 14
Available-for-sale securities, maturing after one year through five years, amortized cost		169
Available-for-sale securities, maturing after five years through ten years, amortized cost		352
Available-for-sale securities, maturing after ten years, amortized cost
Available-for-sale securities, total, amortized cost		$ 535
Available-for-sale securities, maturing in one year or less, weighted-average yield		6.94%
Available-for-sale securities, maturing in one year or less, fair value		$ 16
Available for sale securities, maturing after one year through five years, weighted-average yield		3.13%
Available-for-sale securities, maturing after one year through five years, fair value		$ 172
Available-for-sale securities, maturing after five years through ten years, weighted-average yield		2.86%
Available-for-sale securities, maturing after five years through ten years, fair value		$ 358
Available-for-sale securities, maturing after ten years, fair value
Available-for-sale securities, total, weighted-average yield		3.05%
Available-for-sale securities, total, fair value		$ 546
Available-for-sale securities, maturing in one year or less, weighted-average maturity in years		7 months 6 days
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 6
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years		3 years 4 months 24 days
Held-to-maturity securities, maturing after five years through ten years, amortized cost		$ 2
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years		5 years 6 months
Held-to-maturity securities, total, amortized cost		$ 8
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, weighted-average maturity in years		1 month 6 days
Held to maturity securities, maturing after one year through five years, fair value		$ 9
Held-to-maturity securities, maturing after one year through five years, weighted-average maturity in years		3 years 3 months 18 days
Held-to-maturity securities, maturing after five years through ten years, fair value		$ 2
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, fair value		$ 6
Held-to-maturity securities, maturing after ten years, weighted-average maturity in years		17 years 9 months 18 days
Held-to-maturity securities, total, fair value		$ 17
Held-to-maturity securities, total, weighted-average maturity in years		3 years 10 months 24 days
Held-to-maturity securities, maturing in one year or less, weighted-average yield		1.07%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield		1.15%
Held-to-maturity securities, maturing after five years through ten years, weighted-average yield		1.14%
Held-to-maturity securities, maturing after ten years, weighted-average yield		1.16%
Held-to-maturity securities, total, weighted-average yield		1.15%
Amortized Cost of Investment Securities		$ 543	$ 558
Amortized Cost of Investment Securities, Percentage		0.50%	0.50%
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		$ 2,388
Available-for-sale securities, maturing after one year through five years, amortized cost		1,114
Available-for-sale securities, maturing after five years through ten years, amortized cost		1,369
Available-for-sale securities, maturing after ten years, amortized cost		347
Available-for-sale securities, total, amortized cost		$ 5,218	$ 5,149
Available-for-sale securities, maturing in one year or less, weighted-average yield		7.03%
Available-for-sale securities, maturing in one year or less, fair value		$ 2,422
Available for sale securities, maturing after one year through five years, weighted-average yield		6.71%
Available-for-sale securities, maturing after one year through five years, fair value		$ 1,175
Available-for-sale securities, maturing after five years through ten years, weighted-average yield		5.37%
Available-for-sale securities, maturing after five years through ten years, fair value		$ 1,458
Available-for-sale securities, maturing after ten years, weighted-average yield		5.35%
Available-for-sale securities, maturing after ten years, fair value		$ 368
Available-for-sale securities, total, weighted-average yield		6.42%
Available-for-sale securities, total, fair value		$ 5,423	5,316
Available-for-sale 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, amortized cost		$ 1
Available-for-sale securities, maturing after one year through five years, weighted-average maturity in years		1 year 10 months 24 days
Held-to-maturity securities, maturing after five years through ten years, amortized cost		$ 7
Available-for-sale securities, maturing after five years through ten years, weighted-average maturity in years		7 years 10 months 24 days
Held-to-maturity securities, maturing after ten years, amortized cost
Available-for-sale securities, maturing after ten years, weighted -average maturity in years		10 years 8 months 12 days
Held-to-maturity securities, total, amortized cost		$ 8	8
Available-for-sale securities, total, weighted-average maturity in years		3 years 4 months 24 days
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, fair value		$ 1
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, fair value		$ 7
Held-to-maturity securities, maturing after five years through ten years, weighted-average maturity in years		9 years 3 months 18 days
Held-to-maturity securities, maturing after ten years, fair value
Held-to-maturity securities, maturing after ten years, weighted-average maturity in years		10 years 4 months 24 days
Held-to-maturity securities, total, fair value		$ 8	8
Held-to-maturity securities, total, weighted-average maturity in years		8 years 9 months 18 days
Held-to-maturity securities, maturing in one year or less, weighted-average yield		7.77%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield		8.14%
Held-to-maturity securities, maturing after five years through ten years, weighted-average yield		2.61%
Held-to-maturity securities, maturing after ten years, weighted-average yield		8.09%
Held-to-maturity securities, total, weighted-average yield		3.24%
Amortized Cost of Investment Securities		$ 5,226	$ 5,157
Amortized Cost of Investment Securities, Percentage		4.90%	4.90%
Other Debt Securities and Obligations of Foreign Governments [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, maturing in one year or less, amortized cost
Available-for-sale securities, maturing after one year through five years, amortized cost
Available-for-sale securities, maturing after five years through ten years, amortized cost
Available-for-sale securities, maturing after ten years, amortized cost		678
Available-for-sale securities, total, amortized cost		678
Available-for-sale securities, maturing in one year or less, fair value
Available-for-sale securities, maturing after one year through five years, fair value
Available-for-sale securities, maturing after five years through ten years, fair value
Available-for-sale securities, maturing after ten years, weighted-average yield		2.80%
Available-for-sale securities, maturing after ten years, fair value		$ 608
Available-for-sale securities, total, weighted-average yield		2.80%
Available-for-sale securities, total, fair value		$ 608
Held-to-maturity securities, maturing in one year or less, amortized cost		7
Held-to-maturity securities, maturing after one year through five years, amortized cost		$ 20
Available-for-sale securities, maturing after ten years, weighted -average maturity in years		17 years 1 month 6 days
Held-to-maturity securities, total, amortized cost		$ 27
Available-for-sale securities, total, weighted-average maturity in years		17 years 1 month 6 days
Held-to-maturity securities, maturing in one year or less, fair value		$ 7
Held-to-maturity securities, maturing in one year or less, weighted-average maturity in years		7 months 6 days
Held to maturity securities, maturing after one year through five years, fair value		$ 19
Held-to-maturity securities, maturing after one year through five years, weighted-average maturity in years		4 years
Held-to-maturity securities, total, fair value		$ 26
Held-to-maturity securities, total, weighted-average maturity in years		3 years 1 month 6 days
Held-to-maturity securities, maturing in one year or less, weighted-average yield		1.99%
Held-to-maturity securities, maturing after one year through five years, weighted-average yield		1.40%
Held-to-maturity securities, total, weighted-average yield		1.55%
Amortized Cost of Investment Securities		$ 792	$ 891
Amortized Cost of Investment Securities, Percentage		0.70%	0.80%
Other Investments Including Perpetual Preferred Securities [Member]
Contractual Maturities of Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost		$ 87
Available-for-sale securities, total, weighted-average yield		5.07%
Available-for-sale securities, total, fair value		$ 138
Held-to-maturity securities, total, amortized cost
Available-for-sale securities, total, weighted-average maturity in years		10 years 7 months 6 days
Held-to-maturity securities, total, fair value

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