Investment Securities (Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Securities Available for Sale and Held to Maturity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Available for sale securities:
Amortized Cost	$ 50,572	$ 77,627
Gross Unrealized Gains	120	176
Gross Unrealized Losses	104	438
Fair Value	50,588	77,365
Held to maturity securities:
Amortized Cost	107,971	75,203
Gross Unrealized Gains	461	336
Gross Unrealized Losses	1,050	1,095
Fair Value	107,382	74,444
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	19,301	33,167
Gross Unrealized Gains	50	120
Gross Unrealized Losses	30	92
Fair Value	19,321	33,195
Held to maturity securities:
Amortized Cost	90,154	72,439
Gross Unrealized Gains	397	324
Gross Unrealized Losses	1,040	1,086
Fair Value	89,511	71,677
Asset-backed securities [Member]
Available for sale securities:
Amortized Cost	11,418	20,520
Gross Unrealized Gains	39	29
Gross Unrealized Losses	10	214
Fair Value	11,447	20,335
Held to maturity securities:
Amortized Cost	11,950	941
Gross Unrealized Gains	18	0
Gross Unrealized Losses	2	0
Fair Value	11,966	941
Corporate debt securities [Member]
Available for sale securities:
Amortized Cost	7,482	9,850
Gross Unrealized Gains	24	20
Gross Unrealized Losses	1	18
Fair Value	7,505	9,852
Held to maturity securities:
Amortized Cost	3,179	436
Gross Unrealized Gains	16	0
Gross Unrealized Losses	0	0
Fair Value	3,195	436
U.S. Treasury securities [Member]
Available for sale securities:
Amortized Cost	8,480	8,679
Gross Unrealized Gains	5	3
Gross Unrealized Losses	55	59
Fair Value	8,430	8,623
Held to maturity securities:
Amortized Cost	223	223
Gross Unrealized Gains	0	0
Gross Unrealized Losses	3	4
Fair Value	220	219
U.S. agency notes [Member]
Available for sale securities:
Amortized Cost	1,915	1,915
Gross Unrealized Gains	0	0
Gross Unrealized Losses	8	8
Fair Value	1,907	1,907
Certificates of deposit [Member]
Available for sale securities:
Amortized Cost	1,720	2,070
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	1
Fair Value	1,722	2,071
Held to maturity securities:
Amortized Cost	200
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	200
U.S. state and municipal securities [Member]
Available for sale securities:
Amortized Cost		1,167
Gross Unrealized Gains		2
Gross Unrealized Losses		46
Fair Value		1,123
Held to maturity securities:
Amortized Cost	1,170	68
Gross Unrealized Gains	20	1
Gross Unrealized Losses	0	1
Fair Value	1,190	68
Commercial paper [Member]
Available for sale securities:
Amortized Cost	213	214
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	213	214
Held to maturity securities:
Amortized Cost	99	99
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	99	99
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities:
Amortized Cost	43	45
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	43	45
Held to maturity securities:
Amortized Cost	996	997
Gross Unrealized Gains	10	11
Gross Unrealized Losses	5	4
Fair Value	$ 1,001	$ 1,004

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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