Income Taxes - Net Deferred Tax Balances (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards	$ 499	$ 448
Deferred tax assets:
Allowance for credit losses	312	251
Accrued expense, net	143	159
Unrealized losses on pension and postretirement benefits	233	260
Unrealized net losses on securities available for sale	32	132
Fair value adjustments for valuation of FDIC covered assets	40	53
Deferred Tax Assets, Hedging Transactions	41	78
Other	30	0
Total deferred tax assets	1,330	1,381
Deferred tax liabilities:
Leasing and renewable energy	515	619
Intangible assets	17	59
Pension liabilities	373	365
Other	0	10
Total deferred tax liabilities	905	1,053
Net deferred tax asset	$ 425	$ 328