Securities - Available for Sale Securities (Unrealized Loss Position) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Gross unrealized losses	$ 227	$ 54
Fair value less than 12 months, total temporarily impaired securities	24,038	9,204
Gross unrealized losses less than 12 months, total temporarily impaired securities	497	78
Fair value 12 months or longer, total temporarily impaired securities	1,931	4,529
Gross unrealized losses 12 months or longer, total temporarily impaired securities	62	130
Fair value, total temporarily impaired securities	25,969	13,733
Gross unrealized losses, total temporarily impaired securities	559	208
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	182
Gross unrealized losses, less than 12 months	4
Fair value, 12 months or longer	0
Gross unrealized losses, 12 months or longer	0
Fair Value	182
Gross unrealized losses, Total	4
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	12,345	5,190
Gross unrealized losses, less than 12 months	231	43
Fair value, 12 months or longer	1,410	3,206
Gross unrealized losses, 12 months or longer	44	95
Fair Value	13,755	8,396
Gross unrealized losses, Total	275	138
Held-to-maturity Securities, Fair Value less than 12 months	7,028	1,793
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	156	16
Held-to-maturity Securities, Fair Value 12 months or longer	518	1,320
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	17	34
Held-to-maturity Securities, Fair Value	7,546	3,113
Held-to-maturity Securities, Gross unrealized losses	173	50
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Gross unrealized losses	5	4
Residential Mortgage Backed Securities [Member] \| Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	1,452	1,670
Gross unrealized losses, less than 12 months	17	15
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer	0	0
Fair Value	1,452	1,670
Gross unrealized losses, Total	17	15
Held-to-maturity Securities, Fair Value less than 12 months	547	547
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	5	4
Held-to-maturity Securities, Fair Value 12 months or longer	0	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	0	0
Held-to-maturity Securities, Fair Value	547	547
Held-to-maturity Securities, Gross unrealized losses	5	4
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	1,482
Gross unrealized losses, less than 12 months	35
Fair value, 12 months or longer	0
Gross unrealized losses, 12 months or longer	0
Fair Value	1,482
Gross unrealized losses, Total	35
Held-to-maturity Securities, Fair Value less than 12 months	996
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	49
Held-to-maturity Securities, Fair Value 12 months or longer	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	0
Held-to-maturity Securities, Fair Value	996
Held-to-maturity Securities, Gross unrealized losses	49
Commercial Mortgage Backed Securities [Member] \| Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Gross unrealized losses	49	0
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value, less than 12 months	2	0
Gross unrealized losses, less than 12 months	0	0
Fair value, 12 months or longer	3	3
Gross unrealized losses, 12 months or longer	1	1
Fair Value	5	3
Gross unrealized losses, Total	1	1
Held-to-maturity Securities, Fair Value less than 12 months	4	4
Held-to-maturity Securities, Gross unrealized losses, less than 12 months	0	0
Held-to-maturity Securities, Fair Value 12 months or longer	0	0
Held-to-maturity Securities, Gross unrealized losses, 12 months or longer	0	0
Held-to-maturity Securities, Fair Value	4	4
Held-to-maturity Securities, Gross unrealized losses	0	0
Gross unrealized losses, available for sale securities	1	1
Gross unrealized losses, held-to-maturity securities	$ 1	$ 1

Available for sale and held to maturity securities continuous unrealized loss position aggregate losses.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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