Investment Securities - Summary of Unrealized Loss Positions on Investment Securities (Details) $ in Millions	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Agency - Commercial
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	$ 35	$ 148
Unrealized Loss Position with Duration Under 12 Months	$ 91	$ 303
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	4,000,000	17,000,000
Unrealized Loss Position with Duration Under 12 Months | security	9,000,000	19,000,000
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0	$ (3)
Unrealized Loss Position with Duration Under 12 Months	(1)	0
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	3	148
Unrealized Loss Position with Duration Under 12 Months	$ 5	$ 85
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	1,000,000	13,000,000
Unrealized Loss Position with Duration Under 12 Months | security	1,000,000	6,000,000
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0	$ (1)
Unrealized Loss Position with Duration Under 12 Months	0	0
Agency - Residential
Fair Value
Unrealized Loss Position with Duration 12 Months and Over		266
Unrealized Loss Position with Duration Under 12 Months		$ 148
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security		26,000,000
Unrealized Loss Position with Duration Under 12 Months | security		14,000,000
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over		$ (3)
Unrealized Loss Position with Duration Under 12 Months		(1)
Fair Value
Unrealized Loss Position with Duration 12 Months and Over		35
Unrealized Loss Position with Duration Under 12 Months		$ 38
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security		7,000,000
Unrealized Loss Position with Duration Under 12 Months | security		10,000,000
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over		$ (1)
Unrealized Loss Position with Duration Under 12 Months		0
Corporate debt obligations
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	0
Unrealized Loss Position with Duration Under 12 Months	$ 21
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	0
Unrealized Loss Position with Duration Under 12 Months | security	5,000,000
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0
Unrealized Loss Position with Duration Under 12 Months	(1)
Municipal obligations
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	0	8
Unrealized Loss Position with Duration Under 12 Months	$ 0	$ 0
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	1,000,000	3,000,000
Unrealized Loss Position with Duration Under 12 Months | security	0	0
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0	$ 0
Unrealized Loss Position with Duration Under 12 Months	$ 0	$ 0