Share-Based Associate Compensation Plans (Restricted Stock Unit Information) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) peers_exceeded Peers $ / shares shares	Dec. 31, 2016 USD ($) peers_exceeded Peers $ / shares shares	Dec. 31, 2015 USD ($) peers_exceeded Peers
Reconciliation of Restricted Stock Activity [Line Items]
Number of peers exceeded | peers_exceeded	5	5	4
Number of peers | Peers	9	9	10
Restricted Stock Units (RSUs) | Service Based Shares
Nonvested shares
Beginning balance (in shares)	888,000
Granted (in shares)	292,000
Vested (in shares)	(311,000)
Forfeited or canceled (in shares)	(26,000)
Ending balance (in shares)	843,000	888,000
Weighted-average grant-date fair value
Beginning balance (in dollars per share) | $ / shares	$ 48.59
Granted (in dollars per share) | $ / shares	65.16
Vested (in dollars per share) | $ / shares	43.05
Forfeited or canceled (in dollars per share) | $ / shares	55.59
Ending balance (in dollars per share) | $ / shares	$ 56.16	$ 48.59
Restricted Stock Units (RSUs) | Performance Based Shares
Nonvested shares
Beginning balance (in shares)	236,000
Granted (in shares)	57,000
Vested (in shares)	(87,000)
Forfeited or canceled (in shares)	0
Ending balance (in shares)	206,000	236,000
Weighted-average grant-date fair value
Beginning balance (in dollars per share) | $ / shares	$ 49.64
Granted (in dollars per share) | $ / shares	43.26
Vested (in dollars per share) | $ / shares	36.73
Forfeited or canceled (in dollars per share) | $ / shares	0.00
Ending balance (in dollars per share) | $ / shares	$ 53.35	$ 49.64
Restricted Stock Units (RSUs) | Service Based Shares
Reconciliation of Restricted Stock Activity [Line Items]
Awards vesting period	3 years
Awards other than options vested, intrinsic value | $	$ 23	$ 23	$ 26
Restricted Stock Units (RSUs) | Performance Based Shares
Reconciliation of Restricted Stock Activity [Line Items]
Awards vesting period	3 years
Awards other than options vested, intrinsic value | $	$ 7	$ 6	$ 6
share based performance metric for performance shares	3 years
Risk-free rates, minimum	0.00%	0.00%	0.00%
Risk-free rates, maximum	200.00%	200.00%	200.00%
Shares, Issued	87,228	25,461