Retirement and Benefit Plans (Plan Assets Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure
Securities	[1]	$ 185	$ 172
Equity securities
Defined Benefit Plan Disclosure
Securities	[1]	73	56	[2]
Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Securities	[1]	82	97
Mutual and exchange-traded funds | Money market funds
Defined Benefit Plan Disclosure
Securities	[1]	7	6
Mutual and exchange-traded funds | International funds
Defined Benefit Plan Disclosure
Securities	[1]	30	31
Mutual and exchange-traded funds | Domestic funds
Defined Benefit Plan Disclosure
Securities	[1]	29	39
Mutual and exchange-traded funds | Debt funds
Defined Benefit Plan Disclosure
Securities	[1]	1	5
Mutual and exchange-traded funds | Alternative strategies
Defined Benefit Plan Disclosure
Securities	[1]	10	10
Mutual and exchange-traded funds | Commodity funds
Defined Benefit Plan Disclosure
Securities	[1]	5	6
Debt securities
Defined Benefit Plan Disclosure
Securities	[1]	30	19
Debt securities | U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Securities	[1]	10	8
Debt securities | Agency mortgage-backed securities | Residential mortgage-backed securities
Defined Benefit Plan Disclosure
Securities	[1]	1	1
Debt securities | Agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Securities	[1]	2	2
Debt securities | Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Securities		1
Debt securities | Asset-backed securities and other debt securities
Defined Benefit Plan Disclosure
Securities	[1],[3]	16	8
Fair value level 1
Defined Benefit Plan Disclosure
Securities	[1]	94	76
Fair value level 1 | Equity securities
Defined Benefit Plan Disclosure
Securities	[1]	73	56	[2]
Fair value level 1 | Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Securities	[1]	13	13
Fair value level 1 | Mutual and exchange-traded funds | Money market funds
Defined Benefit Plan Disclosure
Securities	[1]	7	6
Fair value level 1 | Mutual and exchange-traded funds | Alternative strategies
Defined Benefit Plan Disclosure
Securities	[1]	1	1
Fair value level 1 | Mutual and exchange-traded funds | Commodity funds
Defined Benefit Plan Disclosure
Securities	[1]	5	6
Fair value level 1 | Debt securities
Defined Benefit Plan Disclosure
Securities	[1]	8	7
Fair value level 1 | Debt securities | U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Securities	[1]	8	7
Fair value level 2
Defined Benefit Plan Disclosure
Securities	[1]	91	96
Fair value level 2 | Mutual and exchange-traded funds
Defined Benefit Plan Disclosure
Securities	[1]	69	84
Fair value level 2 | Mutual and exchange-traded funds | International funds
Defined Benefit Plan Disclosure
Securities	[1]	30	31
Fair value level 2 | Mutual and exchange-traded funds | Domestic funds
Defined Benefit Plan Disclosure
Securities	[1]	29	39
Fair value level 2 | Mutual and exchange-traded funds | Debt funds
Defined Benefit Plan Disclosure
Securities	[1]	1	5
Fair value level 2 | Mutual and exchange-traded funds | Alternative strategies
Defined Benefit Plan Disclosure
Securities	[1]	9	9
Fair value level 2 | Debt securities
Defined Benefit Plan Disclosure
Securities	[1]	22	12
Fair value level 2 | Debt securities | U.S. Treasury and federal agencies securities
Defined Benefit Plan Disclosure
Securities	[1]	2	1
Fair value level 2 | Debt securities | Agency mortgage-backed securities | Residential mortgage-backed securities
Defined Benefit Plan Disclosure
Securities	[1]	1	1
Fair value level 2 | Debt securities | Agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Securities	[1]	2	2
Fair value level 2 | Debt securities | Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Defined Benefit Plan Disclosure
Securities		1
Fair value level 2 | Debt securities | Asset-backed securities and other debt securities
Defined Benefit Plan Disclosure
Securities	[1],[3]	$ 16	$ 8

[1] For further information on fair value hierarchy levels, refer to Note 1 .

[2] Includes holdings in Bancorp common stock.

[3] Includes corporate bonds.