Significant Accounting Policies Significant Accounting Policies Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Minimum [Member]
Significant Accounting Policies [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals		$ 1,000
Cash Proceeds from BOLI/COLI [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		3	$ 17
Cash Premiums Paid on BOLI/COLI [Member] [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		127	202
Contingent Consideration Paid Up to Amount of Acquisition Date Fair Value [Member] [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		0	13
Contingent Consideration Paid in Excess of Acquisition Date Fair Value [Member] [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 0	$ 10
Stranded Tax Effects in AOCI [Member]
Significant Accounting Policies [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 154