Parent and Guarantor Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	$ 799			$ 844
Interest-bearing Deposits in Banks and Other Financial Institutions	3,125			3,408
Cash and Cash Equivalents, at Carrying Value	3,924			4,252	$ 4,377
Equity Securities	521			518
Available-for-sale securities	23,296			22,303
Held-to-maturity securities	2,089			1,899
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	328			108
Loans and Leases Receivable, Gross	125,544			122,893	120,528
Loans to nonbank subsidiary	0			0
Financing Receivable, Allowance for Credit Losses	1,257	$ 1,278		1,276	1,225	$ 1,155	$ 1,144
Loans and Leases Receivable, Net Amount	124,287			121,617
Property Subject to or Available for Operating Lease, Net	8,639			8,741
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	2,247			2,047
Other Assets	6,014			5,663
Assets	171,345			167,148	164,345
Noninterest-bearing deposit liabilities	153			108
Interest-bearing Deposit Liabilities	98,581			93,148
Deposits	98,734			93,256
Short-term Debt	7,108			11,413
Long-term Debt	47,328			44,226
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	568			375
Unearned Premiums	2,957			2,604
Accounts Payable and Accrued Liabilities	1,511			1,780
Liabilities	158,206			153,654
Stockholders' Equity Attributable to Parent	13,139		$ 13,375	13,494	13,473		$ 13,317
Liabilities and Equity	171,345			167,148
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	49			74
Interest-bearing Deposits in Banks and Other Financial Institutions	6			5
Cash and Cash Equivalents, at Carrying Value	1,071			1,217	1,441
Equity Securities	0			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			0
Loans and Leases Receivable, Gross	5,647			7,434
Loans to nonbank subsidiary	786			879
Financing Receivable, Allowance for Credit Losses	128			185
Loans and Leases Receivable, Net Amount	6,305			8,128
Property Subject to or Available for Operating Lease, Net	10			19
Receivables from bank subsidiary	106			80
Receivables from nonbank subsidiary	61			71
Investment in bank subsidiaries	16,163			16,962
Investment in nonbank subsidiaries	7,162			8,111
Premiums receivable and other insurance assets	0			0
Other Assets	2,123			2,207
Assets	33,001			36,795
Noninterest-bearing deposit liabilities	0			0
Interest-bearing Deposit Liabilities	6			12
Deposits	6			12
Short-term Debt	2,666			3,171
Long-term Debt	15,571			17,966
Debt Payable To Bank Subsidiaries	57			74
Debt Payable To Nonbank Subsidiaries	973			1,103
Payables to Bank Subsidiaries				4
Payables to Nonbank Subsidiaries	130			132
Interest payable	192			200
Unearned Premiums	0			0
Accounts Payable and Accrued Liabilities	267			639
Liabilities	19,862			23,301
Stockholders' Equity Attributable to Parent	13,139			13,494
Liabilities and Equity	33,001			36,795
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	0
Equity Securities	0			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			0
Loans and Leases Receivable, Gross	0			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	16,163			16,962
Investment in nonbank subsidiaries	0			0
Premiums receivable and other insurance assets	0			0
Other Assets	0			0
Assets	16,163			16,962
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	16,163			16,962
Liabilities and Equity	16,163			16,962
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and Due from Banks	750			770
Interest-bearing Deposits in Banks and Other Financial Institutions	3,119			3,403
Cash and Cash Equivalents, at Carrying Value	4,438			4,868	3,493
Equity Securities	521			518
Available-for-sale securities	23,296			22,303
Held-to-maturity securities	2,146			1,973
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	328			108
Loans and Leases Receivable, Gross	119,897			115,459
Loans to nonbank subsidiary	405			408
Financing Receivable, Allowance for Credit Losses	1,129			1,091
Loans and Leases Receivable, Net Amount	119,173			114,776
Property Subject to or Available for Operating Lease, Net	8,629			8,722
Receivables from bank subsidiary	0			0
Receivables from nonbank subsidiary	88			77
Investment in bank subsidiaries	0			0
Investment in nonbank subsidiaries	0			0
Premiums receivable and other insurance assets	2,247			2,082
Other Assets	5,129			5,105
Assets	165,995			160,532
Noninterest-bearing deposit liabilities	153			108
Interest-bearing Deposit Liabilities	98,575			93,136
Deposits	99,744			94,383
Short-term Debt	4,442			8,242
Long-term Debt	31,757			26,260
Debt Payable To Bank Subsidiaries	0			0
Debt Payable To Nonbank Subsidiaries	786			879
Payables to Bank Subsidiaries				0
Payables to Nonbank Subsidiaries	129			127
Interest payable	376			175
Unearned Premiums	2,957			2,604
Accounts Payable and Accrued Liabilities	2,479			2,790
Liabilities	142,670			135,460
Stockholders' Equity Attributable to Parent	23,325			25,072
Liabilities and Equity	165,995			160,532
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			0
Affiliated Entity [Member] | Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	1,016			1,138
Interest-bearing Deposit Liabilities	0			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			0
Affiliated Entity [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	569			695
Interest-bearing Deposit Liabilities	1,016			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	(1,585)			(1,833)	$ (557)
Equity Securities	0			0
Available-for-sale securities	0			0
Held-to-maturity securities	(57)			(74)
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	0			0
Loans and Leases Receivable, Gross	0			0
Loans to nonbank subsidiary	(1,191)			(1,287)
Financing Receivable, Allowance for Credit Losses	0			0
Loans and Leases Receivable, Net Amount	(1,191)			(1,287)
Property Subject to or Available for Operating Lease, Net	0			0
Receivables from bank subsidiary	(106)			(80)
Receivables from nonbank subsidiary	(149)			(148)
Investment in bank subsidiaries	(32,326)			(33,924)
Investment in nonbank subsidiaries	(7,162)			(8,111)
Premiums receivable and other insurance assets	0			(35)
Other Assets	(1,238)			(1,649)
Assets	(43,814)			(47,141)
Noninterest-bearing deposit liabilities	0			0
Interest-bearing Deposit Liabilities	0			0
Deposits	(1,016)			(1,139)
Short-term Debt	0			0
Long-term Debt	0			0
Debt Payable To Bank Subsidiaries	(57)			(74)
Debt Payable To Nonbank Subsidiaries	(1,759)			(1,982)
Payables to Bank Subsidiaries				(4)
Payables to Nonbank Subsidiaries	(259)			(259)
Interest payable	0			0
Unearned Premiums	0			0
Accounts Payable and Accrued Liabilities	(1,235)			(1,649)
Liabilities	(4,326)			(5,107)
Stockholders' Equity Attributable to Parent	(39,488)			(42,034)
Liabilities and Equity	(43,814)			(47,141)
Consolidation, Eliminations [Member] | Affiliated Entity [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Interest-bearing Deposits in Banks and Other Financial Institutions	(1,585)			(1,833)
Interest-bearing Deposit Liabilities	$ (1,016)			$ (1,139)