Earnings Per Common Share Shares Repurchase (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 25, 2018	Sep. 30, 2015
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	6,028,959	61,920	71,506
Share Repurchase Program 1 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount					$ 300
Average price paid per share of Class A Common Stock repurchased	$ 76.70
Shares excluded from weighted average basic shares outstanding	2,242,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 0
Share Repurchase Program 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 500
Average price paid per share of Class A Common Stock repurchased	$ 77.03
Shares excluded from weighted average basic shares outstanding	125,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 340
Class A Common Stock [Member] | Share Repurchase Program 1 [Member]
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	3,910,000
Class A Common Stock [Member] | Share Repurchase Program 2 [Member]
Equity, Class of Treasury Stock [Line Items]
Class A Common Stock repurchased	2,080,000