Investment Securities (Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss, Available for Sale) (Details) $ in Millions	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	$ 29,156	$ 38,165
Available for sale securities: Less than 12 months Unrealized Losses	212	341
Available for sale securities: 12 months or longer Fair Value	12,921	6,644
Available for sale securities: 12 months or longer Unrealized Losses	226	91
Available for sale securities: Total Fair Value	42,077	44,809
Available for sale securities: Total Unrealized Losses	$ 438	$ 432
Number of available for sale securities in unrealized loss positions \| security	627	409
U.S. agency mortgage-backed securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	$ 14,816	$ 8,541
Available for sale securities: Less than 12 months Unrealized Losses	69	47
Available for sale securities: 12 months or longer Fair Value	2,931	813
Available for sale securities: 12 months or longer Unrealized Losses	23	1
Available for sale securities: Total Fair Value	17,747	9,354
Available for sale securities: Total Unrealized Losses	92	48
Asset-backed securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	1,670	17,127
Available for sale securities: Less than 12 months Unrealized Losses	13	240
Available for sale securities: 12 months or longer Fair Value	9,237	2,743
Available for sale securities: 12 months or longer Unrealized Losses	201	66
Available for sale securities: Total Fair Value	10,907	19,870
Available for sale securities: Total Unrealized Losses	214	306
Corporate debt securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	2,407	5,433
Available for sale securities: Less than 12 months Unrealized Losses	17	25
Available for sale securities: 12 months or longer Fair Value	653	942
Available for sale securities: 12 months or longer Unrealized Losses	1	6
Available for sale securities: Total Fair Value	3,060	6,375
Available for sale securities: Total Unrealized Losses	18	31
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	6,926	5,010
Available for sale securities: Less than 12 months Unrealized Losses	59	17
Available for sale securities: 12 months or longer Fair Value
Available for sale securities: 12 months or longer Unrealized Losses
Available for sale securities: Total Fair Value	6,926	5,010
Available for sale securities: Total Unrealized Losses	59	17
U.S. agency notes [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	1,907	1,281
Available for sale securities: Less than 12 months Unrealized Losses	8	10
Available for sale securities: 12 months or longer Fair Value		1,547
Available for sale securities: 12 months or longer Unrealized Losses		17
Available for sale securities: Total Fair Value	1,907	2,828
Available for sale securities: Total Unrealized Losses	8	27
Certificates of deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	474	773
Available for sale securities: Less than 12 months Unrealized Losses		2
Available for sale securities: 12 months or longer Fair Value	100	599
Available for sale securities: 12 months or longer Unrealized Losses	1	1
Available for sale securities: Total Fair Value	574	1,372
Available for sale securities: Total Unrealized Losses	1	$ 3
U.S. state and municipal securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities: Less than 12 months Fair Value	956
Available for sale securities: Less than 12 months Unrealized Losses	46
Available for sale securities: 12 months or longer Fair Value
Available for sale securities: 12 months or longer Unrealized Losses
Available for sale securities: Total Fair Value	956
Available for sale securities: Total Unrealized Losses	$ 46

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Publisher FASB
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