Investment Securities Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale Without an Allowance for Credit Losses) (Details) $ in Millions	Jun. 30, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	$ (95)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	5,513
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(37)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	1,188
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(132)
Debt securities, available-for-sale, unrealized loss position	6,701
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(7)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	2,124
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	249
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(10)
Debt securities, available-for-sale, unrealized loss position	2,373
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(8)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	213
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(6)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	81
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(14)
Debt securities, available-for-sale, unrealized loss position	294
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	136
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(3)
Debt securities, available-for-sale, unrealized loss position	136
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(61)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	2,107
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(2)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	71
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(63)
Debt securities, available-for-sale, unrealized loss position	2,178
Asset backed [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(18)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	969
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(22)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	616
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(40)
Debt securities, available-for-sale, unrealized loss position	1,585
Other [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(1)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	100
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(1)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	35
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(2)
Debt securities, available-for-sale, unrealized loss position	$ 135