Parent and Guarantor Consolidating Financial Statements (Schedule of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	$ 844		$ 1,547
Interest-bearing Deposits in Banks and Other Financial Institutions	3,408		4,387
Cash and Cash Equivalents, at Carrying Value	4,252		5,934
Trading Securities			0
Available-for-sale securities	22,821		18,926
Held-to-maturity securities	1,899		839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	108		0
Loans and Leases Receivable, Gross	122,893		118,944
Loans to bank subsidiary			0
Loans to nonbank subsidiary	0		0
Financing Receivable, Allowance for Credit Losses	1,276		1,144	$ 1,054
Loans and Leases Receivable, Net Amount	121,617		117,800
Property Subject to or Available for Operating Lease, Net	8,741		11,470
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	0		0
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,047		1,905
Other Assets	5,663		6,854
Assets	167,148		163,728	158,581
Noninterest-bearing deposit liabilities	108		84
Interest-bearing Deposit Liabilities	93,148		78,938
Deposits	93,256		79,022
Short-term Debt	11,413		12,673
Long-term Debt	44,226		54,128
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	0		0
Payables to Bank Subsidiaries		$ 0
Payables to Nonbank Subsidiaries	0		0
Interest payable	375		351
Unearned Premiums	2,604		2,500
Accounts Payable and Accrued Liabilities	1,780		1,737
Liabilities	153,654		150,411
Stockholders' Equity Attributable to Parent	13,494		13,317	$ 13,439	$ 15,399
Liabilities and Equity	167,148		163,728
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	74		720
Interest-bearing Deposits in Banks and Other Financial Institutions	5		100
Cash and Cash Equivalents, at Carrying Value	1,217		820
Trading Securities			0
Available-for-sale securities	0		0
Held-to-maturity securities	0		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Gross	7,434		4,705
Loans to bank subsidiary			1,125
Loans to nonbank subsidiary	879		1,779
Financing Receivable, Allowance for Credit Losses	185		115
Loans and Leases Receivable, Net Amount	8,128		7,494
Property Subject to or Available for Operating Lease, Net	19		42
Receivables from bank subsidiary	80		299
Receivables from nonbank subsidiary	71		107
Investment in bank subsidiaries	16,962		17,727
Investment in nonbank subsidiaries	8,111		10,318
Premiums receivable and other insurance assets	0		0
Other Assets	2,207		4,347
Assets	36,795		41,154
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	12		167
Deposits	12		167
Short-term Debt	3,171		3,622
Long-term Debt	17,966		21,798
Debt Payable To Bank Subsidiaries	74		330
Debt Payable To Nonbank Subsidiaries	1,103		1,027
Payables to Bank Subsidiaries		4
Payables to Nonbank Subsidiaries	132		153
Interest payable	200		253
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	639		487
Liabilities	23,301		27,837
Stockholders' Equity Attributable to Parent	13,494		13,317
Liabilities and Equity	36,795		41,154
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	0		0
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Cash and Cash Equivalents, at Carrying Value	0		0
Trading Securities			0
Available-for-sale securities	0		0
Held-to-maturity securities	0		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Gross	0		0
Loans to bank subsidiary			0
Loans to nonbank subsidiary	0		0
Financing Receivable, Allowance for Credit Losses	0		0
Loans and Leases Receivable, Net Amount	0		0
Property Subject to or Available for Operating Lease, Net	0		0
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	0		0
Investment in bank subsidiaries	16,962		17,727
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	0		0
Other Assets	0		0
Assets	16,962		17,727
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	0		0
Deposits	0		0
Short-term Debt	0		0
Long-term Debt	0		0
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	0		0
Payables to Bank Subsidiaries		0
Payables to Nonbank Subsidiaries	0		0
Interest payable	0		0
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	0		0
Liabilities	0		0
Stockholders' Equity Attributable to Parent	16,962		17,727
Liabilities and Equity	16,962		17,727
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	770		827
Interest-bearing Deposits in Banks and Other Financial Institutions	3,403		4,287
Cash and Cash Equivalents, at Carrying Value	4,868		5,515
Trading Securities			82
Available-for-sale securities	22,821		19,253
Held-to-maturity securities	1,973		839
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	108
Loans and Leases Receivable, Gross	115,459		114,239
Loans to bank subsidiary			0
Loans to nonbank subsidiary	408		626
Financing Receivable, Allowance for Credit Losses	1,091		1,029
Loans and Leases Receivable, Net Amount	114,776		113,836
Property Subject to or Available for Operating Lease, Net	8,722		11,428
Receivables from bank subsidiary	0		0
Receivables from nonbank subsidiary	77		67
Investment in bank subsidiaries	0		0
Investment in nonbank subsidiaries	0		0
Premiums receivable and other insurance assets	2,082		1,936
Other Assets	5,105		5,085
Assets	160,532		158,041
Noninterest-bearing deposit liabilities	108		84
Interest-bearing Deposit Liabilities	93,136		78,771
Deposits	94,383		78,855
Short-term Debt	8,242		9,051
Long-term Debt	26,260		32,330
Debt Payable To Bank Subsidiaries	0		0
Debt Payable To Nonbank Subsidiaries	879		2,903
Payables to Bank Subsidiaries		0
Payables to Nonbank Subsidiaries	127		351
Interest payable	175		98
Unearned Premiums	2,604		2,500
Accounts Payable and Accrued Liabilities	2,790		3,911
Liabilities	135,460		129,999
Stockholders' Equity Attributable to Parent	25,072		28,042
Liabilities and Equity	160,532		158,041
Affiliated Entity [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Interest-bearing Deposit Liabilities	0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	1,138		0
Interest-bearing Deposit Liabilities	0
Affiliated Entity [Member] | Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Interest-bearing Deposit Liabilities	0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	695		401
Interest-bearing Deposit Liabilities	1,139
Consolidation, Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	0		0
Interest-bearing Deposits in Banks and Other Financial Institutions	0		0
Cash and Cash Equivalents, at Carrying Value	(1,833)		(401)
Trading Securities			(82)
Available-for-sale securities	0		(327)
Held-to-maturity securities	(74)		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0
Loans and Leases Receivable, Gross	0		0
Loans to bank subsidiary			(1,125)
Loans to nonbank subsidiary	(1,287)		(2,405)
Financing Receivable, Allowance for Credit Losses	0		0
Loans and Leases Receivable, Net Amount	(1,287)		(3,530)
Property Subject to or Available for Operating Lease, Net	0		0
Receivables from bank subsidiary	(80)		(299)
Receivables from nonbank subsidiary	(148)		(174)
Investment in bank subsidiaries	(33,924)		(35,454)
Investment in nonbank subsidiaries	(8,111)		(10,318)
Premiums receivable and other insurance assets	(35)		(31)
Other Assets	(1,649)		(2,578)
Assets	(47,141)		(53,194)
Noninterest-bearing deposit liabilities	0		0
Interest-bearing Deposit Liabilities	0		0
Deposits	(1,139)		0
Short-term Debt	0		0
Long-term Debt	0		0
Debt Payable To Bank Subsidiaries	(74)		(330)
Debt Payable To Nonbank Subsidiaries	(1,982)		(3,930)
Payables to Bank Subsidiaries		$ (4)
Payables to Nonbank Subsidiaries	(259)		(504)
Interest payable	0		0
Unearned Premiums	0		0
Accounts Payable and Accrued Liabilities	(1,649)		(2,661)
Liabilities	(5,107)		(7,425)
Stockholders' Equity Attributable to Parent	(42,034)		(45,769)
Liabilities and Equity	(47,141)		(53,194)
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	(1,833)		$ (401)
Interest-bearing Deposit Liabilities	$ (1,139)