Shareholders' Equity - Shares Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended					4 Months Ended	12 Months Ended	76 Months Ended
	May 09, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	May 09, 2019	Dec. 31, 2018	May 09, 2019	May 10, 2019	Feb. 27, 2019
Equity, Class of Treasury Stock [Line Items]
Repurchases of common stock		$ 80				$ 100
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares)		1,908,605	2,992,932	3,299,049	4,163,190	2,787,936		13,243,107
Repurchases of common stock		$ 79	$ 120	$ 130	$ 152	$ 98		$ 500
Average price paid per share (in dollars per share)		$ 41.62	$ 40.09	$ 39.41	$ 36.48	$ 35.20		$ 37.76
Remaining capacity of shares repurchase program											$ 300
Subsequent Event [Member] | Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased (in shares)	853,432						2,762,037		97,317,994
Repurchases of common stock	$ 40						$ 119		$ 2,835
Average price paid per share (in dollars per share)	$ 46.25						$ 43.05		$ 29.13
Remaining capacity of shares repurchase program										$ 279