Derivative Financial Instruments - Notional Amount, Estimated Fair Value and Maturity of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Other liabilities
Liabilities
Notional Amount		$ 6,938
Fair Value		39
Designated as hedging instrument | Other assets
Assets
Notional Amount	$ 300
Fair Value	0
Designated as hedging instrument | Interest rate swaps on FHLB advances | Other assets
Assets
Notional Amount	200
Fair Value	0
Designated as hedging instrument | Interest rate swaps on AFS securities | Other assets
Assets
Notional Amount	100
Fair Value	0
Designated as hedging instrument | Interest rate swaps on CDs | Other assets
Assets
Notional Amount		20
Fair Value		0
Designated as hedging instrument | Interest rate swaps on CDs | Other liabilities
Liabilities
Notional Amount		10
Fair Value		0
Not designated as hedging instrument
Assets
Fair Value	28	27
Liabilities
Fair Value	17	39
Not designated as hedging instrument | Other assets
Assets
Notional Amount	7,137	4,493
Fair Value	62	47
Not designated as hedging instrument | Other liabilities
Liabilities
Notional Amount	7,640
Fair Value	18
Not designated as hedging instrument | Futures
Liabilities
Fair Value		1
Not designated as hedging instrument | Futures | Other assets
Assets
Notional Amount	550	248
Fair Value	0	0
Not designated as hedging instrument | Futures | Other liabilities
Liabilities
Notional Amount		1,513
Fair Value		1
Not designated as hedging instrument | Mortgage-backed securities forwards
Assets
Fair Value	2	4
Liabilities
Fair Value	9	31
Not designated as hedging instrument | Mortgage-backed securities forwards | Other assets
Assets
Notional Amount	1,918	362
Fair Value	2	4
Not designated as hedging instrument | Mortgage-backed securities forwards | Other liabilities
Liabilities
Notional Amount	5,749	4,625
Fair Value	9	31
Not designated as hedging instrument | Rate lock commitments | Other assets
Assets
Notional Amount	3,870	2,221
Fair Value	34	20
Not designated as hedging instrument | Rate lock commitments | Other liabilities
Liabilities
Notional Amount	229	45
Fair Value	1	0
Not designated as hedging instrument | Interest rate swaps and swaptions
Assets
Fair Value	26	23
Not designated as hedging instrument | Interest rate swaps and swaptions | Other assets
Assets
Notional Amount	799	1,662
Fair Value	26	23
Not designated as hedging instrument | Interest rate swaps and swaptions
Liabilities
Fair Value	8	7
Not designated as hedging instrument | Interest rate swaps and swaptions | Other liabilities
Liabilities
Notional Amount	1,662	755
Fair Value	$ 8	$ 7