Investment Securities - Summary of Unrealized Loss Positions on Investment Securities (Details) $ in Millions	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Agency - Commercial
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	$ 835	$ 1,025
Unrealized Loss Position with Duration Under 12 Months	$ 0	$ 1
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	57	74
Unrealized Loss Position with Duration Under 12 Months | security	0	1
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ (12)	$ (43)
Unrealized Loss Position with Duration Under 12 Months	0	0
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	286	336
Unrealized Loss Position with Duration Under 12 Months	$ 0	$ 0
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	23	26
Unrealized Loss Position with Duration Under 12 Months | security	0	0
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ (5)	$ (13)
Unrealized Loss Position with Duration Under 12 Months	0	0
Agency - Residential
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	395	647
Unrealized Loss Position with Duration Under 12 Months	$ 0	$ 14
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	39	79
Unrealized Loss Position with Duration Under 12 Months | security	0	5
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ (5)	$ (24)
Unrealized Loss Position with Duration Under 12 Months	0	0
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	104	345
Unrealized Loss Position with Duration Under 12 Months	$ 14	$ 0
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	19	60
Unrealized Loss Position with Duration Under 12 Months | security	2	0
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ (1)	$ (9)
Unrealized Loss Position with Duration Under 12 Months	0	0
Municipal obligations
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	13	28
Unrealized Loss Position with Duration Under 12 Months	$ 6	$ 1
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	5	16
Unrealized Loss Position with Duration Under 12 Months | security	1	2
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0	$ (1)
Unrealized Loss Position with Duration Under 12 Months	0	0
Corporate debt obligations
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	0	0
Unrealized Loss Position with Duration Under 12 Months	$ 0	$ 7
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	0	0
Unrealized Loss Position with Duration Under 12 Months | security	0	2
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0	$ 0
Unrealized Loss Position with Duration Under 12 Months	0	$ 0
Other MBS
Fair Value
Unrealized Loss Position with Duration 12 Months and Over	0
Unrealized Loss Position with Duration Under 12 Months	$ 13
Number of Securities
Unrealized Loss Position with Duration 12 Months and Over | security	0
Unrealized Loss Position with Duration Under 12 Months | security	1
Unrealized Loss
Unrealized Loss Position with Duration 12 Months and Over	$ 0
Unrealized Loss Position with Duration Under 12 Months	$ 0