Goodwill and Other Intangible Assets, net (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) intangible_asset	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Finite-Lived Intangible Assets [Line Items]
Number of intangible assets reclassified | intangible_asset	3
Intangible assets, pre-tax amortization expense		$ 88	$ 74	$ 82
Estimated amortization expense, year one, assuming no additional transactions occur that require the amortization of intangible assets		84
Estimated amortization expense, year two, assuming no additional transactions occur that require the amortization of intangible assets		84
Estimated amortization expense, year three, assuming no additional transactions occur that require the amortization of intangible assets		84
Estimated amortization expense, year four, assuming no additional transactions occur that require the amortization of intangible assets		84
Estimated amortization expense, year five, assuming no additional transactions occur that require the amortization of intangible assets		$ 84
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Increase to amortizable intangible assets	$ 153
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Decrease to non-amortizable intangible assets	$ 153