Share-Based Compensation Plans (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012		Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation expense	$ 68		$ 50		$ 137		$ 105
Restricted stock units (“RSUs”) [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation expense	40		34		95		83
Non-vested share awards
Non-vested at beginning of period (in shares)					10,432		9,916		9,916
Granted (in shares)					3,505		4,706
Vested (in shares)					(3,345)		(2,986)
Forfeited (in shares)					(229)		(356)
Non-vested at end of period (in shares)	10,363		11,280		10,363		11,280
Weighted Average Fair value
Non-vested at beginning of period (in dollars per share)					$ 44	[1]	$ 42	[1]	$ 42	[1]
Granted (in dollars per share)					$ 62	[1]	$ 45	[1]
Vested (in dollars per share)					$ 44	[1]	$ 42	[1]
Forfeited (in dollars per share)					$ 45	[1]	$ 44	[1]
Non-vested at end of period (in dollars per share)	$ 50	[1]	$ 44	[1]	$ 50	[1]	$ 44	[1]
Target PSAs granted					3,505		4,706
Fair value					$ 62	[1]	$ 45	[1]
Performance share awards (“PSAs”) [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation expense	27		13		38		15
Non-vested share awards
Granted (in shares)					1,135				1,369		1,715
Weighted Average Fair value
Granted (in dollars per share)					$ 58	[2]			$ 47	[2]	$ 50	[2]
Target PSAs granted					1,135				1,369		1,715
Fair value					$ 58	[2]			$ 47	[2]	$ 50	[2]
Number of shares that would be issued based on current performance levels					1,135				1,958		1,339
Unamortized expense, based on current performance levels	59				59				49		11
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation expense	0		1		1		3
Employee stock purchase plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation expense	$ 1		$ 2		$ 3		$ 4
Minimum [Member] | Performance share awards (“PSAs”) [Member]
Weighted Average Fair value
Vesting conditions period					1 year
Percent of shares issued	0.00%				0.00%
Maximum [Member] | Performance share awards (“PSAs”) [Member]
Weighted Average Fair value
Vesting conditions period					5 years
Percent of shares issued	200.00%				200.00%

[1] Represents per share weighted average fair value of award at date of grant

[2] Represents per share weighted average fair value of award at date of grant.