Retirement Plans (Schedule of Valuation of the Company's Pension Plan Assets by Pricing Categories) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 370	$ 308
(Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	289	240
(Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32	30
(Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49	38
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	7
Cash and cash equivalents | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4	7
Cash and cash equivalents | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121	100
Equity securities | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104	83
Equity securities | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	17
Equity securities | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34	127
Corporate debt securities | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	127
Corporate debt securities | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	0
Corporate debt securities | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	211	74
Other | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	148	23
Other | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	13
Other | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 49	$ 38