Investment Securities - Fair Value and Unrealized Losses on AFS Investment Securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value
Less Than 12 Months	$ 261	$ 460
12 Months or Longer	41	783
Total	302	1,243
Unrealized Losses
Less Than 12 Months	(2)	(15)
12 Months or Longer	0	(24)
Total	(2)	(39)
U.S. government and government sponsored entities
Fair Value
Less Than 12 Months	0	3
12 Months or Longer	3	16
Total	3	19
Unrealized Losses
Less Than 12 Months	0	0
12 Months or Longer	0	0
Total	0	0
Obligations of states, municipalities, and political subdivisions
Fair Value
Less Than 12 Months	29	10
12 Months or Longer	4	57
Total	33	67
Unrealized Losses
Less Than 12 Months	(1)	0
12 Months or Longer	0	(1)
Total	(1)	(1)
Commercial paper
Fair Value
Less Than 12 Months	76
12 Months or Longer	0
Total	76
Unrealized Losses
Less Than 12 Months	0
12 Months or Longer	0
Total	0
Non-U.S. government and government sponsored entities
Fair Value
Less Than 12 Months	19	19
12 Months or Longer	14	97
Total	33	116
Unrealized Losses
Less Than 12 Months	0	(1)
12 Months or Longer	0	(1)
Total	0	(2)
Corporate debt
Fair Value
Less Than 12 Months	63	377
12 Months or Longer	13	448
Total	76	825
Unrealized Losses
Less Than 12 Months	(1)	(14)
12 Months or Longer	0	(18)
Total	(1)	(32)
RMBS
Fair Value
Less Than 12 Months	45	23
12 Months or Longer	0	78
Total	45	101
Unrealized Losses
Less Than 12 Months	0	0
12 Months or Longer	0	(2)
Total	0	(2)
CMBS
Fair Value
Less Than 12 Months	15	10
12 Months or Longer	7	54
Total	22	64
Unrealized Losses
Less Than 12 Months	0	0
12 Months or Longer	0	(1)
Total	0	(1)
CDO/ABS
Fair Value
Less Than 12 Months	14	18
12 Months or Longer	0	33
Total	14	51
Unrealized Losses
Less Than 12 Months	0	0
12 Months or Longer	0	(1)
Total	$ 0	$ (1)