Investment Securities (Contractual Maturity of Debt Securities) (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 55,269,000,000	$ 43,181,000,000
Available-for-sale Securities, Fair value, Total	55,760,000,000	44,235,000,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	854,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	7,441,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	7,872,000,000
Available for Sale Securities, Amortized Cost, After 10 years	38,512,000,000
Securities available for sale, amortized cost	54,679,000,000	42,739,000,000
Available-for-sale Securities, Fair value, 1 year or less	861,000,000
Available-for-sale Securities, Fair value, After 1 year through 5 years	7,497,000,000
Available-for-sale Securities, Fair value, After 5 years through 10 years	7,926,000,000
Available-for-sale Securities, Fair value, After 10 years	38,887,000,000
Available-for-sale Securities, Fair value, Total	$ 55,171,000,000	43,794,000,000
Weighted-average yield, GAAP basis, available for sale securities	2.73%
Held to Maturity Securities, Amortized Cost, 1 year or less	$ 119,000,000
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	1,083,000,000
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	1,991,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	11,575,000,000
Held to Maturity Securities, Amortized Cost, Total	14,768,000,000	11,588,000,000
Held-to-maturity Securities, Fair Value, 1 year or less	119,000,000
Held-to-maturity Securities, Fair Value, After 1 year through 5 years	1,112,000,000
Held-to-maturity Securities, Fair Value, After 5 years through 10 years	2,059,000,000
Held-to-maturity Securities, Fair Value, After 10 years	11,712,000,000
Held-to-maturity Securities, Debt Maturities, Fair Value, Total	$ 15,002,000,000	$ 11,984,000,000
Weighted-average yield, GAAP basis, held to maturity securities	3.42%
One Year or Less [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.76%
Weighted-average yield, GAAP basis, held to maturity securities	3.02%
After One Year Through Five Years [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.23%
Weighted-average yield, GAAP basis, held to maturity securities	3.41%
After Five Years Through Ten Years [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.28%
Weighted-average yield, GAAP basis, held to maturity securities	3.18%
After Ten Years [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.91%
Weighted-average yield, GAAP basis, held to maturity securities	3.46%
US Treasury and Government Agencies Securities [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	$ 586,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	4,172,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	4,234,000,000
Available for Sale Securities, Amortized Cost, After 10 years	772,000,000
Securities available for sale, amortized cost	9,764,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	258,000,000
Held to Maturity Securities, Amortized Cost, Total	258,000,000
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	99,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	986,000,000
Available for Sale Securities, Amortized Cost, After 10 years	23,613,000,000
Securities available for sale, amortized cost	24,698,000,000
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	4,000,000
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	321,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	9,227,000,000
Held to Maturity Securities, Amortized Cost, Total	9,552,000,000
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	3,000,000
Available for Sale Securities, Amortized Cost, After 10 years	3,989,000,000
Securities available for sale, amortized cost	3,992,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	233,000,000
Held to Maturity Securities, Amortized Cost, Total	233,000,000
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	22,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	109,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	232,000,000
Available for Sale Securities, Amortized Cost, After 10 years	1,554,000,000
Securities available for sale, amortized cost	1,917,000,000
Held to Maturity Securities, Amortized Cost, 1 year or less	119,000,000
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	810,000,000
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	142,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	57,000,000
Held to Maturity Securities, Amortized Cost, Total	1,128,000,000
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	50,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	28,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	8,000,000
Available for Sale Securities, Amortized Cost, After 10 years	4,816,000,000
Securities available for sale, amortized cost	4,902,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	722,000,000
Held to Maturity Securities, Amortized Cost, Total	722,000,000
Asset backed [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	9,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	1,526,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	1,787,000,000
Available for Sale Securities, Amortized Cost, After 10 years	2,095,000,000
Securities available for sale, amortized cost	5,417,000,000
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	3,000,000
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	590,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	124,000,000
Held to Maturity Securities, Amortized Cost, Total	717,000,000
State and Municipal [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	1,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	127,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	336,000,000
Available for Sale Securities, Amortized Cost, After 10 years	1,518,000,000
Securities available for sale, amortized cost	1,982,000,000
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	62,000,000
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	938,000,000
Held to Maturity Securities, Amortized Cost, After 10 years	954,000,000
Held to Maturity Securities, Amortized Cost, Total	1,954,000,000
Other Debt Securities [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	186,000,000
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	1,377,000,000
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	289,000,000
Available for Sale Securities, Amortized Cost, After 10 years	155,000,000
Securities available for sale, amortized cost	2,007,000,000
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	204,000,000
Held to Maturity Securities, Amortized Cost, Total	$ 204,000,000