Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale) (Details) - Debt Securities [Member] - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	$ (181)	$ (410)
AFS unrealized loss position less than 12 months - fair value	17,460	25,760
AFS unrealized loss position 12 months or more - unrealized loss	(104)	(126)
AFS unrealized loss position 12 months or more - fair value	4,791	6,287
Total AFS unrealized loss	(285)	(536)
Total AFS fair value	22,251	32,047
HTM unrealized loss position less than 12 months - unrealized loss	(118)	(187)
HTM unrealized loss position less than 12 months - fair value	7,509	8,425
HTM unrealized loss position 12 months or more - unrealized loss	(12)	(10)
HTM unrealized loss position 12 months or more - fair value	207	613
Total HTM unrealized loss	(130)	(197)
Total HTM fair value	7,716	9,038
US Treasury and Government Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(41)	(57)
AFS unrealized loss position less than 12 months - fair value	2,872	3,108
AFS unrealized loss position 12 months or more - unrealized loss	(1)	(20)
AFS unrealized loss position 12 months or more - fair value	310	2,028
Total AFS unrealized loss	(42)	(77)
Total AFS fair value	3,182	5,136
HTM unrealized loss position less than 12 months - unrealized loss	(12)	(22)
HTM unrealized loss position less than 12 months - fair value	448	238
Total HTM unrealized loss	(12)	(22)
Total HTM fair value	448	238
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(126)	(267)
AFS unrealized loss position less than 12 months - fair value	12,005	16,942
AFS unrealized loss position 12 months or more - unrealized loss	(44)	(20)
AFS unrealized loss position 12 months or more - fair value	1,911	922
Total AFS unrealized loss	(170)	(287)
Total AFS fair value	13,916	17,864
HTM unrealized loss position less than 12 months - unrealized loss	(97)	(153)
HTM unrealized loss position less than 12 months - fair value	6,908	8,041
HTM unrealized loss position 12 months or more - unrealized loss	(5)	(8)
HTM unrealized loss position 12 months or more - fair value	138	161
Total HTM unrealized loss	(102)	(161)
Total HTM fair value	7,046	8,202
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss		(1)
AFS unrealized loss position less than 12 months - fair value	41	109
AFS unrealized loss position 12 months or more - unrealized loss	(22)	(51)
AFS unrealized loss position 12 months or more - fair value	412	1,119
Total AFS unrealized loss	(22)	(52)
Total AFS fair value	453	1,228
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(9)	(33)
AFS unrealized loss position less than 12 months - fair value	1,105	1,577
AFS unrealized loss position 12 months or more - unrealized loss	(20)	(1)
AFS unrealized loss position 12 months or more - fair value	719	86
Total AFS unrealized loss	(29)	(34)
Total AFS fair value	1,824	1,663
HTM unrealized loss position less than 12 months - fair value	93
HTM unrealized loss position 12 months or more - fair value	2
Total HTM fair value	95
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(1)	(14)
AFS unrealized loss position less than 12 months - fair value	214	880
AFS unrealized loss position 12 months or more - unrealized loss	(6)	(13)
AFS unrealized loss position 12 months or more - fair value	388	987
Total AFS unrealized loss	(7)	(27)
Total AFS fair value	602	1,867
HTM unrealized loss position less than 12 months - fair value	1
Total HTM fair value	1
Asset backed [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(1)	(5)
AFS unrealized loss position less than 12 months - fair value	623	1,317
AFS unrealized loss position 12 months or more - unrealized loss	(3)	(17)
AFS unrealized loss position 12 months or more - fair value	436	902
Total AFS unrealized loss	(4)	(22)
Total AFS fair value	1,059	2,219
HTM unrealized loss position 12 months or more - unrealized loss		(2)
HTM unrealized loss position 12 months or more - fair value		451
Total HTM unrealized loss		(2)
Total HTM fair value		451
Other debt [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS unrealized loss position less than 12 months - unrealized loss	(3)	(33)
AFS unrealized loss position less than 12 months - fair value	600	1,827
AFS unrealized loss position 12 months or more - unrealized loss	(8)	(4)
AFS unrealized loss position 12 months or more - fair value	615	243
Total AFS unrealized loss	(11)	(37)
Total AFS fair value	1,215	2,070
HTM unrealized loss position less than 12 months - unrealized loss	(9)	(12)
HTM unrealized loss position less than 12 months - fair value	59	146
HTM unrealized loss position 12 months or more - unrealized loss	(7)
HTM unrealized loss position 12 months or more - fair value	67	1
Total HTM unrealized loss	(16)	(12)
Total HTM fair value	$ 126	$ 147