Commercial Paper and Long-term Debt (Narrative) (Details)
3 Months Ended 12 Months Ended
Jul. 02, 2017
USD ($)
Dec. 31, 2018
USD ($)
lenders
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Nov. 30, 2015
USD ($)
Long-term Debt [Line Items]          
Commercial paper   $ 300,000,000 $ 300,000,000    
Commercial Paper, Weighted Average Interest Rate   2.954% 1.583%    
Commercial Paper, Weighted Average Original Maturity Period   16 days 20 days    
Commercial paper, maximum original maturity period   90 days      
Repayments of Debt $ 591,000,000        
Loss on repayment of long-term debt 39,000,000 $ 0 $ 39,000,000 $ 0  
Loss on repayment of long-term debt, net of tax $ 25,000,000        
Line of Credit Facility, Maximum Borrowing Capacity         $ 1,250,000,000
Debt Instrument, Basis Spread on Variable Rate   0.805%      
Number of highly rated lenders | lenders   20      
Aggregate Maximum Percentage Of Any Single Lender   10.00%      
Borrowings outstanding on long-term line of credit   $ 0 0    
Outstanding letters of credit   0 0    
Line of Credit Facility, Remaining Borrowing Capacity   $ 950,000,000      
Ratio of indebtedness to net capital   0.306      
Total payments for interest on commercial paper and long-term debt   $ 194,000,000 $ 214,000,000 $ 231,000,000  
Maximum [Member]          
Long-term Debt [Line Items]          
Ratio of indebtedness to net capital   0.60